Even though social networking companies serve tens of millions of users, there’s still bizarrely little advertising on the most popular sites. Many big agencies and brands have experimented, but they’re still looking for better ways to target the users they want.

The latest company hoping to serve these advertisers is Appssavvy, a startup that sells direct advertising space on social media applications like Flixster, MesmoTV, and Playfish — most of which have a presence on major sites like Facebook. The company announced today that it received $3.1 million in second round funding.

New York-based Appssavvy joins a field of peers hoping to score social media ad dollars. Companies like SocialMedia, Lookery and Social Cash have also been selling advertisers on new and innovative ways to add branding to social networking sites. But Appssavvy likes to distinguish itself as a consulting firm, working with its clients to devise a more custom, targeted end product.

Examples of Appssavvy campaigns include Sony’s sponsorship of Facebook’s Wedding Book application to promote its film “Made of Honor,” a custom Facebook application built for Kohl’s back-to-school season, and ads for the TBS show “My Boys” on the MesmoTV application… on Facebook. Okay yes, all of their examples are from Facebook, but Appssavvy says it can also hook brands up with apps for the iPhone, MySpace, Hi5, etc.

Despite the seemingly thin client base represented on the startup’s site, it did land a deal with NBC Universal at the start of the month that gave it exclusive ad-sale rights on NBC News’ iCue website. iCue is a social network targeted at students that lets members watch NBC archive footage, join related discussions, and play relevant learning games.

Even if Appssavvy can bag other big names, it still faces a tough market for social media campaigns, which have yet to gain major traction on Madison Avenue. In fact, one study suggests that half of these campaigns are already set up to fail.

Still, that didn’t dissuade Appssavvy’s recent investors. The round was led by True Ventures and also included About.com founder Scott Kumit.