New York-based agency holding company Omnicom Group has bought a stake in Chinese marketing firm Shunya Communications Group to strengthen its presence in China’s ad market, the Wall Street Journal reported. Exact terms of the purchase were not disclosed. Shunya, which has a client list on the mainland including Mercedes-Benz, Huihou TCL Computer and GE, will become affiliated with Omnicom firms, including its advertising agency, BBDO.