While group messaging has become popular, particularly among adolescents, it has not yet been explored in the HCI literature. We interviewed 48 adolescents, aged 15-24, who use group messaging regularly. We present a framework for understanding the types of groups they communicate with according to three dimensions: focus, membership, and duration. We also present findings about factors influencing their choice of group messaging tools and the problems they have managing multiple group threads using multiple tools. We explore the problem of notification overload and users’ strategies for managing frequent notifications. We describe one approach of “social alerting, ” when group members notify one another directly, rather than rely on app notifications. We relate our findings to prior work and offer design suggestions to address the challenges our participants faced in managing frequent group notifications.