The coolest college clique to join this year isn't a sorority or the lacrosse team. Students from the University of Southern California to Dartmouth College are lining up to become on-campus volunteer marketers for technology start-ups.

Students are slipping into lecture halls to write brand names and company URLs on professors' white boards, making cold pitches to strangers on college-town streets, creating Facebook pages, producing videos and lobbying school newspapers to plug the businesses of entrepreneurs in New York...