Social game developer Digital Chocolate announced that its games on Facebook, like Millionaire City and MMA Pro Fighter, now reach a total of 12 million monthly active users.

Millionaire City, Digital Chocolate's most popular title, alone has picked up nearly 8.5 million monthly users since its launch last May, according to figures from AppData. The company's catalog of seven titles on the social network collectively attract over two million daily active users.

While those numbers are a fraction of the studio's much bigger rivals like Zynga and Electronic Arts/Playdom, which have monthly audiences of 220+ million and 50+ million respectively, Digital Chocolate claims it's "the only major Facebook publisher to add to its absolute growth at this rate this year".

Furthermore, the developer points to its cross-platform strategy, an initiative that includes the launch of Millionaire City on iPhone and MySpace earlier this month. Since debuting three weeks ago, the game's free iPhone edition has received more than 500,000 downloads.

Digital Chocolate also launched MMA Pro Fighter as a standalone PC game, and has plans to release an iPhone app for the licensed fighting game. The company says it has the advantage of a high cross-promotional scale and the ability to cross-promote its titles on several major platforms (E.g. Facebook, iPhone, MySpace, etc.).

"Digital Chocolate has both the gaming pedigree and technology infrastructure to successfully offer games across all the popular emerging platforms for casual social games," said Trip Hawkins, CEO of Digital Chocolate. "This is really a unique capability, and one which we are still in the early stages of exploiting."