San Francisco — Zynga, the social games firm behind such titles as FarmVille, CityVille and Mafia Wars, has grown users for its new game Empires & Allies to over 30 million in 17 days, including 2 million added on Monday, according to the analyst firm AppData as reported by VentureBeat.

Now one of the fastest-growing games in history, Empires and Allies is also described by Zynga as its “most social” game. Set on a sprawling multi-island game board, Empires & Allies integrates familiar game play elements from popular Zynga titles into a story-driven combat crusade. Empires & Allies is free to Facebook users with the option of paying real money for virtual currency and increased features.

Seven days ago Zynga was reportedly at 249 million monthly active users on Facebook — growing to 267 million on Monday. With talks of Zynga preparing for an initial public offering (IPO), the rapid growth of Empires & Allies — described by AOL Games blog as “Risk meets CityVille,” — could make Zynga’s going public “easier,” opined VentureBeat Monday.

Related Links: (Venture Beat)