Social game makerZynga said it’s launching games on Android-based mobile phones, beginning with Live Poker. The company, which has become famous for its games on Facebook, recently launched games on Apple’s iPhone. Its support for Android is a vote of confidence for the mobile operating system from Google, which is trying to challenge Apple.

Zynga made the announcement at Facebook’s mobile event today.

Zynga launched FarmVille for the iPhone earlier this summer and is developing games for mobile phones in Japan as well. Each time it adds a new platform, it has to figure out if the cost of adapting its games is worth the effort.

Android has been a relatively weak platform for games, largely because of problems with Google’s Android Market. That makes it hard to do well with games that are sold as downloads on Android. But companies such as Rovio have had big hits launching free ad-supported games on Android phones, such as Angry Birds.

San Francisco-based Zynga said it has no other details to announce about the game yet. Zynga’s game will take advantage of single-sign-on, a new feature from Facebook that allows users to avoid typing in numerous user names and passwords to access multiple apps on a mobile phone; instead, users can simply log into their Facebook account, and Facebook will automatically sign them in to other apps.