This study addresses why Japanese teenagers participate in mobilebased word-of-mouth (WOM) campaigns. It is posited that commitment to the promoted brand, relationship with the mobile device, and group–person connectivity act as antecedents of two primary gratifications of the campaign, entertainment value and purposive value, which in turn determine the direction and strength of the attitude–intention–behavior chain. A “real” mobile campaign was used as stimulus. Based on a random sampling method, 22,500 structured questionnaires were sent to young consumers, 13–18 years old, via mobile device. Our data fit the proposed model fairly well, and all hypothesized paths are supported. There are significant differences in the strength of the paths between teenagers who learned of the campaign from non-WOM sources (i.e., content-based Web sites and e-mail magazines) versus WOM sources (pass-along e-mail and direct referral). In closing, theoretical and managerial implications are discussed and important limitations are recognized. © 2008 Wiley Periodicals, Inc.