Reuters reports that social gaming giant Zynga has continued to acquire mobile games developers, as part of its efforts to bolster its performance away from the Facebook platform.

The latest buy took place in December, when it acquired Germany-based developer Gamedoctors. The size of the deal was not revealed.

In its new guise as a publicly listed company, Zynga has also confirmed a number of earlier reported acquisitions. It acquired US-based developers Page44, HipLogic and Astro Ape Studios during 2011, again with the size of the deals remaining confidential.

Zynga was also linked with a number of other buys during 2011, including mobile players Wonderland Studios and Five Mobile.

In a November 2011 regulatory document, Zynga said that there were more than 11.1 million daily active users of its mobile games. The company has identified mobile as a growth driver away from its core internet properties.