Internal memo says exec will be "embarking on a new venture."
Former General Motors exec Nikki Wilson takes on post six months after founder's racist remark.
Publicis' return to organic growth sets high bar for rivals.
Exec succeeds Rob Schwartz, who moves to a newly created post overseeing trio of agency's New York shops.
The creative matching service uses artificial intelligence to link freelancers with agencies and marketing companies seeking talent.