WPP's Martin Sorrell Says Snapchat Could 'Well Be' a Third Digital Ad Competitor to Facebook and Google

His agency contributed $90 million to the app’s 2016 revenue

BARCELONA, SPAIN—As Snapchat gears up to go public tomorrow morning and start trading on the New York Stock Exchange, WPP chief Martin Sorrell sees the app as a legitimate competitor to Google and Facebook for its ad dollars.