Raptr, the gamer social network, just raised $2.50 for every fan that it has. The company announced today that it has built its audience to more than 6 million users and raised $15 million in funding.

The numbers show that Raptr has a very good chance at breaking out of Facebook’s shadow and establishing a niche social network catering just to hardcore gamers. If it can stay the course, the company could become a magnet for marketing games, discovering new titles, and gaining insights into the behavior of gamers, who are a lucrative target for advertisers.

The Mountain View, Calif.-based company is headed by Dennis “Thresh” Fong, who became known earlier in his career as one of the best first-person shooter professional game players. Fong’s visibility is one reason Raptr is also well known in hardcore gamer circles.

Raptr said the service is now adding more than 750,000 new users a month. Monthly unique users are at 5.5 million. In June 2010, Raptr had just 1 million monthly active users.

DAG Ventures raised the second round of funding. Other investors in the new round include new investor Tenaya Capital and existing investor Accel Partners.

Fong said the goal is to turn Raptr into the world’s preeminent gaming community. The company has also expanded onto mobile devices.

To date, Raptr has raised $27 million. Raptr will use the funding to add new features for the community. With Raptr, users can currently share their own achievements with other gamers on the PC, Xbox 360, and the PlayStation 3. They can chat about games, browse the web from within a game, and see what their friends are playing via the phone.

Game publishers can use Raptr to target ads and sell games. And Raptr can help game discovery — one of the biggest challenges in a sea of games on the market — by encouraging friends to share their favorite games with each other. Raptr’s media site partners include GameSpot, GamePro, and 1UP. Those sites can use Raptr’s anonymized data to showcase what games are hot or not.

The company was founded in 2007. It has a number of rivals, but Raptr now has the most funding raised to date.