[Every other week, Gamasutra examines the most popular Facebook games according to monthly active users, looking at the top titles and developers on the social network to see who's attracting or losing players.] Less than two months after its release, Zynga's hidden object game on Facebook is resonating with audiences. It passed other popular Zynga titles like CastleVille, FarmVille, and Words With Friends in the last two weeks, as we predicted. At this rate -- the game is at 30.2 million players and is currently adding nearly 5 million users each week -- it's conceivable that the game will pass Texas HoldEm Poker's current count of 33 million in just a few days, which would make it the second most popular title on the site. It would still have a long way to go before it could match the biggest game on the social network, Zynga's CityVille, which lost 300,000 players in the past two weeks but still has 47.2 million. But it's doing quite well for Zynga's first entry in the hidden object casual game genre! While Hidden Chronicles flourished, the third and fourth most popular Facebook games, CastleVille and FarmVille respectively, saw their userbases shrink. CastleVille went from 31 million users to 29.7 million, as FarmVille dropped from 30 million to 28.4 million. Electronic Arts and Playfish's The Sims Social also lost a substantial number of players recently, dropping from 21.7 million to 20.9 million. Zynga's Words With Friends, though, picked up 1 million new pals as it grew to 20 million monthly users. At #8, Empires & Allies, another Zynga title, added 300,000 users for a 15.7 million total. It was followed by Wooga's Diamond Dash with 15.5 million players (1.2 million new users) and Tetris Online's Tetris Battle with 14 million players (1.5 million new users). You can see the full list of the top 20 Facebook games along with exact monthly active user counts below: All charts and data are courtesy of Facebook application metrics and trends site AppData.