mobstersWhile console video games have moved on to titles like Tekken 6, the social games industry is so new that they’re just getting going with their sequels.

Playdom‘s Mobsters 2: Vendetta, is debuting today on Facebook. The game is the first major follow-up to the Mountain View, Calif.-based company’s Mobsters game, which has been a monster hit on MySpace with 13.5 million users, but which also faces tough competition on Facebook.

The mafia genre is crowded on social networks because its “family style” multiplayer game play is just right for players who want to socialize with their friends. But Playdom wants to take its games a step further. It launched an iPhone version, Mobsters: Big Apple, a couple of weeks ago as an extension of the MySpace game.

The Mobsters 2 game launched less than two weeks ago and has grown to about 140,000 users, said Rachel Thomas, head of marketing at Playdom. Typically, social game companies launch their games quietly, tweak them, and then announce them once growth starts taking off.

Sean Clark, executive producer, says the new Facebook game has received an average rating of four stars and that players are spending 45 minutes a day with it. The art for the game has a “graphic novel” style, or something resembling a dark comic book. The game has about twice the content of the original and some new features.

One feature is a real story about the need to avenge the death of a brother. The game also has a dynamic territory system, where players can build and manage a mob in a city. Players can travel to other territories beyond New York, including Miami and Las Vegas. And there’s an expanded class system, with 20 levels that characters can advance through. The Playdom team designed this whole system in the course of three months, with design led by a video game veteran, Steve Meretzky, a longtime casual game designer who is now vice president of design.

The original Mobsters debuted in July, 2008 on MySpace and became the top app in September. The game still holds the No. 1 spot on MySpace. Playdom launched the original game on Facebook in June. The user numbers for the original Mobsters game on Facebook are small, but Playdom claims triple digit monthly user and revenue growth. The company is moving fast, which is why it plans to grow from less than 100 employees to more than 200 in four months.