Tongal wanted to wrap its head around Snapchat marketing, so in mid-November the crowdsourcing contest platform encouraged its social-media-minded community to contribute ideas for major brands. Five-hundred-eighty-three creative folks quickly pitched campaign concepts, and the 10 most-mentioned brands were (in this order) Facebook, Starbucks, Apple, Coca-Cola, McDonald's, Twitter, Doritos, Google, LEGO and Nike. For the uninitiated, Snapchat, with more than 8 million users, is an increasingly popular app among millennials that lets users send photos and videos—sometimes for sexting&...