As social media is widely adopted in collaborative learning that make team virtual, it is critical for teams to identify and leverage knowledge of team members. Yet little is known how social media influence teams to coordinate their knowledge and collaborate effectively. In this study, we investigate the roles of two kinds of social media activity—information processing and social connection in teamwork by applying communication and transactive memory systems (TMS) as the mechanisms of explicit and implicit coordination respectively. Drawing on the data from a study that involves 40 teams of graduate students performing a complex research report over 8 weeks, we find that both TMS and communication can significantly improve teamwork outcomes. As to social media activities, the results reveal that both information processing and social connection can enhance the level of TMS, however, only social connection is positively related to communication, unfortunately, information processing can’t significantly strengthen communication quality. Possible reasons are discussed and some theoretical and practical implications are also put forward.