Tripwolf, an online travel guide that also offers some social features, has closed a $2.5 million funding round led by European travel publisher MairDumont Group along with investor Dieter von Holtzbrinck, a German entrepreneur who headed the Holtzbrinck Publishing Group for over 20 years.

Tripwolf offers comprehensive travel guides comprised of a mix of professionally written material and user submissions (the site lets members keep travel blogs, upload photos, and leave reviews for individual attractions). Since launching in June 2008 the site has grown to 15,000 members; a modest number but one that will probably grow as the site’s repository of information does.

Tripwolf is also planning to release an iPhone application soon that will include content from published guidebooks. Users will be able to chart out their interary online while still at home, and then can sync their customized travel guides to their phones so they don’t have to worry about data charges abroad. The site is also planning to release versions of the site in French, Spanish, and Italian over the next few months (it is currently available in English and German).

I’m still a little skeptical about Tripwolf – there’s already a plethora of travel information available on the web. But the site’s collection of content from professional guidebooks along with its partnership with the MairDumont Group (which Tripwolf says is the biggest European publisher of travel guides) may give it a leg up on other sites that are primarily user-generated.