Dec 28, 2010 10:42 GMT  ·  By

Barely a month after its launch, Zynga's latest game CityVille has become the most popular app on Facebook, surpassing the famous FarmVille. Close to 70 million people have played CityVille in the past 30 days, according to the latest numbers from AppData. Meanwhile, 'only' 57 million have played FarmVille in the same period.

While CityVille is already Zynga's biggest game and the most popular Faceboook app of all time, it shows no sign of slowing down.

CityVille gained 2.4 million new users in the last day alone and 22 million over the past week. It got to six million users in its first eight days.

FarmVille on the other hand has been holding steady, though it too gained some users in the past month. Zynga's long time superstar isn't going anywhere any time soon, but it may be challenged by the game company's latest creation.

Other games in the "Ville" family haven't fared so well. FrontierVille, launched earlier this year, is the fifth most popular application on Facebook, with over 30 million monthly active users, but compared to CityVille it's only a moderate success. What's more, it seems to be losing players, over 400,000 people have stopped playing FrontierVille in the past week.

For Zynga though, there really is no way to lose. Even if FrontierVille is not doing as well as its other creations, as long as people are playing a "Ville" game, Zynga is making money.

In fact, four out of the top five Facebook apps of the moment are Zynga games. Overall, Zynga is by far the largest developer on the social network with over 270 million monthly active users several times more than the Takeoff Monkey which takes the second spot with 60 million users.

While Zynga has been expanding and looking beyond Facebook, the fact that it makes many of the most popular apps on the site, on which a lot of Facebook users spend a lot of time, shows that may Facebook needs Zynga as much as the other way around.