In traditional face-to-face teamwork, “social loafing” is a significant factor that decreases teamwork performance. We therefore wondered if the same phenomenon takes place in technology-supported teams. An experiment was conducted with 95 online brainstorming teams composed of 286 students from five classes at three universities. The results revealed under what situations social loafing effects exist and how the impacts of team member familiarity, perceived co-worker loafing, and task results visibility work on technologysupported team performance. Discussions and suggestions are provided to enhance academic research on and management of technology-supported teamwork.