Zoosk, the dating service with a focus on social networks, has closed a $30 million Series D funding round led by Bessemer Venture Partners, with existing investors Canaan Partners and ATA Ventures participating as well. Bessemer’s David Cowan will be joining the Zoosk board of directors.

We last covered the company in October, when it reached the 40 million user milestone (12 million of whom are active). The site has been cash flow posistive for the last two months, and is on track for $20 million in revenue this year.

After launching in December 2007, Zoosk gained popularity through its social network applications available on Hi5, Bebo, Friendster, MySpace, and Facebook. It also has a standalone site at Zoosk.com, as well as an AIR client. The site tries to differentiate itself from dating portals like Match.com by getting distribution on as many platforms as possible, as well as by targeting a 25-35 year old demographic.

Cofounders (and co-CEOs) Alex Mehr and Shayan Zadeh say that that the company will use the money to continue building itself into a leading dating site on the web. The company is also planning to further expand to new platforms: soon it will be launching a strong push on mobile, including a new iPhone app. Zoosk may also begin offline marketing efforts to raise awareness.