Social media and in-game advertising startup Offerpal Media has raised $15 million in a second round of funding. D.E. Shaw Ventures led the round; previous backers InterWest Partners and North Bridge Venture Partners also participated. The Fremont, Calif.-based company has raised $19.6 million since it was founded in 2007. Offerpal will use most of the funding to build out its ad platform, which lets brands seed social networks and casual games with “offers” like surveys and trial subscriptions; members can earn points or virtual gifts for completing them.

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The company claims it has more than 2,000 advertisers in its system, including Citibank, and is working with over 800 developers on branded apps across Facebook, MySpace and WeeWorld, among others. CEO Ana Shukla told the NYT that the average app-maker is pulling in $150,000 worth of revenue per month by teaming up with Offerpal, with average CPMs hovering in the $150-$200 range. Competitors include Appsavvvy and SuperRewards. Release.