For background, the AddThis button sharing tool is currently deployed on 9 million websites worldwide and allows users to easily and quickly share content with others through more than 300 social networking services in 70 languages.

Previously, the company’s AddThis button was able to work on mobile sites, but these specialized versions can be used within apps, and are optimized for the native mobile OS. AddThis for iOS and Android is easy for app developers to implement, says Clearspring, because it is designed and optimized specifically for mobile devices.

Further, there is no additional work for publishers wishing to implement AddThis on the mobile web. The same tool used for the website automatically works in the mobile environment.

And AddThis integrates mobile sharing data from native apps and the mobile web with all other sharing data in an analytics dashboard giving publishers a complete view of the impact of social sharing on traffic. AddThis for iOS is available for download now, and developers can sign up for the Android version due out this summer.

Clearspring also just raised $20 million in new funding.

The name Clearspring Technologies may not be terribly familiar to you, but chances are you’ve often clicked on or at least come across its AddThis buttons, which are plastered on publisher sites Web-wide.

The U.S.-based social sharing platform company this morning announced that it has raised a whopping $20 million in a Series D round of funding led by Institutional Venture Partners, with existing backers such as NEA and Novak Biddle Venture Partners participating.

The extra capital injection brings total funding raised by Clearspring to $58 million.

The investment comes as the company, which was founded in 2008, is experiencing rapid growth; Clearspring says it is hiring a new employee almost every week.

The company’s AddThis sharing tool is currently deployed on 9 million websites worldwide, Clearspring says, enabling users to share content with others through more than 300 social networking services in 70 languages.

Sandy Miller, a partner at Institutional Venture Partners, which also invested in high-profile startups like Twitter and Zynga, says Clearspring currently processes some 10 TB of data every day, “as much data per week as the entire digital Library of Congress has stored online”.

Clearspring says the funding will be used to develop new and enhance existing publisher products and bolster its advertising offerings – the company makes money by gathering insights on what large scores of Internet users read and share with their friends in real time, and selling that data to companies who can benefit from these insights (think ad exchange operators and demand-side platform providers). Revenue is on track to triple this year, the company claims, although absolute numbers to back that up were not provided.

The company says it also plans to explore strategic acquisitions (bootstrapped but profitable rival AddToAny springs to mind).

Aside from Institutional Venture Partners, NEA and Novak Biddle Venture Partners, Clearspring investor include former AOL president Ted Leonsis, AOL founder Steve Case, Capital One co-founder Nigel Morris, and Silicon Valley angel investor Ron Conway.

Like Twitter, AddToAny turns five years old this week. It doesn’t garner even a fraction of the attention that venture-backed competitors like Clearspring (AddThis), Gigya and ShareThis do, but it has definitely put its stake in the social sharing widget ground.

Note: the above-cited rivals have raised roughly $90 million combined, while AddToAny has never taken outside financing since it was founded back in 2006.

Still, the AddToAny button is one of the most distributed widgets on the web, and according to the company the most distributed widget from a bootstrapped startup. AddToAny is now even a lucrative business, and has gotten to that point without spending a dime on marketing.

How is the service monetized? AddToAny sells (anonymous) aggregate sharing data, which is used by clients to increase the relevancy of their ads. Income has been admittedly small, but revenue projections for 2012 range in the seven figures.

Being one of the first to offer a social sharing and bookmarking widget for website publishers has helped AddToAny a lot to get where they are now, but there’s more to it than that.

Founder Pat Diven II says he has never felt the need to raise outside funding, although he reckons it might be fairly easy to secure financing if he wanted to. That said, he started AddToAny as a side project and, going forward, wants to keep things simple and stable first and foremost. That strategy has worked wonders for the service given its steady growth rate.

Diven II says that there have been many serious and casual buy-out offers over the years, but that the focus remains squarely on the user and publisher experience rather than ‘exiting’.

Today, AddToAny handles over a billion widget loads and millions of shares every month, and boasts a total reach of over 100 million visitors.

And what has Diven II concluded based on that wealth of data? That over 60 percent of all sharing activity is not to Facebook, Twitter, or email, meaning that (what the entrepreneur calls) “me-too, niche, long-tail, and non-U.S. sharing destinations” still matter.

ShareThis, which you may be familiar with thanks to all the buttons online publishers worldwide have been plastering on their sites to lure you into spreading their content, is now live at roughly 1 million websites, aggregately reaching more than 400 million users.

The company has now tapped Kristen Fergason, formerly a marketer at Yahoo, as its new CMO to grow even more. In addition to her hiring, ShareThis has named Julie Greenhouse SVP Ad Sales & Business Development and Ben Slutter VP of Revenue and Ad Operations.

Both were with the company previously.

ShareThis allows users to share content from anywhere to anyone and also offers a so-called ‘social advertising platform’ called AudienceShare.

Fergason will henceforth lead ShareThis’ overall marketing strategy and execution. She previously held executive roles in marketing and business development at companies like Yahoo, where she was responsible for B2B marketing and industry outreach.

Fergason came to Yahoo with its acquisitions of Maven Networks, where she was VP of Marketing. She was also a member of the Major League Baseball Advanced Media executive team for six years, serving in a similar role.

ShareThis competes with companies like AddThis (which claims installs on 7 million domains and a reach of 1 billion users per month) and Gigya (which claims a reach of more than 280 million users across more than 500,000 sites).

Social sharing is becoming a big contributor to traffic for many sites. While Facebook and Twitter drive more sharing than any other services, Google is trying to compete with Buzz, which is now part of Gmail but shares links to article and blog posts through Google Reader. Over the past month, according to AddThis, sharing through Google Reader is up 35 percent, with a big jump on February 9, the day Buzz launched.  This number only measures sharing through the AddThis button, which is on more than 600,000 Websites and gives you the option to share content through more than 200 services. So it is only a proxy for total sharing on Google Reader, but a decent one.

Google Reader still barely registers when compared to Twitter and Facebook, which account for 31 percent and 8 percent of all sharing via AddThis, respectively.  But Buzz is definitely giving it a boost.

You can now chart how different services do against each other on the sharing front via a new services directory on AddThis. For instance, Google Bookmarks does much better than Google Reader, with 5 percent of all AddThis activity.  It even beats Digg (which has 3 percent).  Google Bookmarks is probably used more for personal bookmarking than for social consumption, but it is smack in the middle of Twitter and Digg when it comes to activity via AddThis.

Another comparison is Tumblr versus Posterous, which suggests that Tumblr  is much more popular as a reposting tool, and is about neck-and-neck with WordPress.

MadKast is an embeddable widget that lets you easily share links with your friends on any of 15 link sharing sites (Digg, Delicious, Reddit, …). But unlike other link-sharing widgets such as AddThis, MadKast also lets you send links via email, SMS, or IM. It’s a rather simple, yet useful, tool for letting your readers spread your posts.

The service launched in October 2006 and announced that the widget was being served over 1 million times per day last month. Tomorrow they’ll announce that they’ve reached the 2 million milestone.

If you’re interested in adding the AddThis widget to your site, the customization tool is here.

AddThis is gathering some very interesting data that can form the core of a business model now that they have fairly deep penetration. They’re releasing some of this data tomorrow – showing the top bookmarking services and feed readers where their users store data (see the graphs below). Given that AddThis also sees what stories people are bookmarking, it wouldn’t be hard to imagine other things they could do with all of this data.

The top bookmarking services, after the browser feature itself (“favorites”) are del.icio.us and Google Bookmarks, followed by Digg and Yahoo My Web. No surprises there. The top feed reader by a large margin is the much improved Google Reader, which is more popular than Yahoo and Bloglines combined. I am surprised at that – Recent Feedburner data suggested Google Reader was doing very well, but not as well as the AddThis data suggests.