[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.] As has been the case in recent weeks, the App Leaderboard for Facebook's games category has pretty much the same top 20 titles as the last edition (with a single exception, Playtika's Slotomania replacing 6waves Lolapps's Ravenskye City at #20). Zynga's CityVille remains at the top spot with 48.8 million monthly active users. That's down from the 49.2 million players the city-building sim had two weeks ago, but it's still way ahead of any other social game on Facebook. CastleVille, Zynga's newest release, continues to see big audience gains, as it's now the second biggest title on the social network with 37.7 million users. Two weeks ago it was at #5 with 26.5 million players, and last week it was at 33.6 million. Two more Zynga titles take the next spots, FarmVille with 32.1 million users (dropping from #2 despite picking up 1.1 million new players in the last two weeks) and Texas HoldEm Poker with 28.8 million players (down from 29.4 million). Electronic Arts's The Sims Social takes #5 with 27.9 million users (down 29.8 million). It's followed by Zynga's Empires & Allies with 16.2 million users (down from 17.8 million) and Words with Friends with 13.5 million (up from 12.5 million). After Wooga's Diamond Dash at #8 with 11.8 million users (up from 11.4 million), there's King.com's Bubble Witch Saga with 9.9 million users (up from 9.2 million) and Wooga's Bubble Island with 9.7 million users (down from 9.8 million). Mafia Wars 2 by Zynga, the company's second most recent release and first numbered sequel, fell to #16 with 6.7 million monthly active users from #10 two weeks ago with 9.7 million players. 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.