Chefville, social readers, Scribd, Causes, BranchOut and more on this week’s top 20 growing Facebook apps by MAU

Zynga’s ChefVille leads our list of the fastest growing Facebook applications by monthly active users this week with 2,141 percent gain that pushed the game past 12 million MAU.

Zynga seems to have put its marketing weight behind Chefville rather than The Ville, which had been a top gainer for several weeks. Now The Ville is the No. 1 app on Facebook overall, but has started to see a decline in users. Last week we noticed that Zynga was promoting Chefville with Facebook’s new search ads, Sponsored Results.