Zynga acquired four mobile game developers in the second half of 2012, Reuters reports.
David Ko, the company's chief mobile officer, disclosed the names of all four companies, but declined to comment on the amount Zynga paid for each.
In August 2011, Zynga acquired the San Francisco-based HipLogic, developer of a proprietary mobile content delivery platform. In the same month, it also bought the New York-based Astro Ape Studios, the developer of hit games like Monsterz Revenge and Office Heroes.
Page44 Studios, also based in San Francisco and best known for its work on the iOS version of World of Goo, joined the company in September. Zynga closed out the year with the acquisition of ZombieSmash developer Gamedoctors, which is based in Germany.
The acquisitions will bolster Zynga's mobile development resources as it continues to expand beyond its principal Facebook business.
The company has launched two games since it went public in December, but neither achieved the level of success expected from Zynga products.
Hidden Chronicles, for example, had 710,000 DAUs after 12 days on release, versus 5 million DAUs for hit Facebook games Castleville and Empires & Allies over a similar period.
Zynga's share-price has faltered since it went public, dropping from the IPO price of $10 to as low as $8 earlier this month. Yesterday, shares traded at a low of $8.59, before closing the day at $8.69.