Electronic Arts and PlayFish's "The Sim Social", has topped the list of fastest growing FaceBook games with more than 50 million users playing the social game last week. The game attracted 15.5 million new users to take the top spot with 51.5 million total monthly players.

"The Sim Social" is based on EA's long running and successful Sims franchise. It is now the second biggest game on the social network just behind Zynga's 74.2 million "CityVille" players. SimSocial is now ahead of "Empire and Allies" with 37.3 million and "Farmville" with 36.5 million players.

The success of SimSocial should worry game company Zynga who makes some of the most popular FaceBook games including the top ranked "Cityville" and "Farmville". EA is confident that it will soon take over the top spot.

"We're very optimistic," John Earner, general manager of PlayFish London said in an interview with Industry Gamers. "At the same time, we, more than anyone, have learned how to be humble in the last two years. We had to relearn a lot of things. Zynga's enjoyed great success in a lot of ways, but we have not been sitting on our thumbs."

"We've been learning. We've been growing. And the last year has been spent focused on this game and I think we've now proven to the market that we've learned what we need to learn to take on Zynga."

EA still has a daunting challenge ahead. Zynga's user base is around 40 million, all of whom play the developer's six of the current top ten social games. That market share makes it easier for Zynga to release new games. Cityville's popularity is based on Zynga's aggressive marketing on its other FaceBook games.

"We got [users] largely through cross-promotion of our Sims title, via our other legacy titles, our PopCap titles or the broader Sims community," Earner said. "And we've begun spending quite a bit of money." There's still plenty left in EA's arsenal though. "We've hardly burned any of our marketing powder and we're already sitting about two million daily users shy of CityVille."

"I'm pretty optimistic...and also am totally confident and I think that Zynga's going to do a great job and I'm going to try to fight to keep that slot. But I think this game's got an amazing shot and I would bet money on it."

Zynga's response is more expansions for Farmville and a sequel to Mafia Wars. It recently launched Adventure World which focuses more on puzzle solving and exploration.