Complex sentence: Tierkel was previously the co-founder of the social citizenship site Localocracy, which was acquired by Huffington Post Media Group in 2011, as well as CMO of the enterprise software company PeopleSoft.
Split into simpler sentences: Tierkel was previously the co-founder of the social citizenship site Localocracy, which was acquired by Huffington Post Media Group in 2011. Tierkel also served as CMO of the enterprise software company PeopleSoft.