Bob Greenberg is working alongside Sir John Hegarty after joining the board of Whalar, a social influencer "dating service".
The R/GA founder, who has been named vice-chairman, knows the start-up well after Whalar entered the R/GA Ventures programme in 2017. The platform is also backed by Snapchat.
Whalar, which describes itself as a "dating service" because the site’s algorithm helps brands find creators for collaboration, has been chaired by Hegarty since 2017.
Greenberg, meanwhile, stood down as R/GA chief executive in January. He remains executive chairman of the Interpublic agency and has committed to staying "active" at the company until 2020 at least.
Since being founded in 2016 by Neil Waller and James Street, Whalar has 100 staff in New York, London, Berlin and Singapore, and has worked with brands including Apple, Disney and Unilever.
Other board members include Roxanne Taylor, former chief marketing officer at Accenture, and Rob Horler, former US chief executive at Dentsu Aegis Network, who is joining as president and chief operating officer.