Steven Cao, the CEO of Edelman China, has been absent from work for over a week, after "cooperating with authorities" on the investigation of his former business partner Rui Chenggang.
Rui, a popular CCTV host, was detained over corruption allegations in mid-July.
Edelman confirmed to Marketing in an email that it had lost contact with its CEO, adding further information about his whereabouts was not immediately available.
Cao and Rui Chenggang founded PR firm Pegasus Communications, which Edelman acquired a majority stake in 2007.
On 13 July, the celebrity CCTV business host was detained by Chinese authorities for alleged corruption allegations.
On the same day, one of Edelman's PR firm Pegasus was embroiled in the media sting with a tweed on People's Daily Twitter account saying Rui held part of the shares in the agency.
Edelman then distanced itself with an e-mail reply saying Rui no longer has any shareholding in Pegasus after the agency acquired all of his remaining shares in 2010.