[Every other week, Gamasutra examines the fastest-growing Facebook games according to monthly active users, looking at which titles and developers are having the most success attracting new players on the social network.] Zynga's Hidden Chronicles, the developer's latest title and its first entry in the popular "hidden object" casual gaming genre, continues to enjoy rapid growth and is now the fifth post popular game on Facebook, behind other Zynga staples like CityVille, Texas HoldEm Poker, CastleVille, and FarmVille. In just the last seven days, Hidden Chronicles has gained 6.6 million players. It's racked up a total of 25.3 million users since launching in early January, and could overtake FarmVille (28.4 million total) and CastleVille (30.5 million) in terms of audience size this week, if it continues to grow at this rate. Social Point's gender-based strategy game Social Wars is the second fastest-growing game this week with 900,000 new players and a 2.8 million total. It's followed by Fruit Ninja Frenzy, a social game version of Halfbrick's smartphone hit Fruit Ninja, which doubled its size last week to 1.8 million total users. At #4, Texas HoldEm Poker added 800,000 card players to its already hefty 32.5 million count. After that, there's GameHouse's Uno with 750,000 users and a 1.4 million total, and Wooga's Diamond Dash with 700,000 users and a 14.6 million total. Tetris Online's Tetris Battle (14.6 million total) and King.com's Bubble Witch Saga (13.1 million) both gained 600,000 new users last week. Zynga's Empires & Allies (13.1 million), Manuel Otto's Stick Run (2.8 million), and Wooga's Bubble Island (10.7 million) attracted 500,000 new players each. The full list of the top 20 fastest growing Facebook games along with exact monthly active user counts, are as follows: All charts and data are courtesy of Facebook application metrics and trends site AppData.