During the COVID-19 pandemic, undergraduates found themselves in an unprecedented social situation. Campuses across North America closed, as universities moved to remote learning. When in-person classes resumed, students had to negotiate the return to on-campus life. The current investigation examines predictive associations between pandemic-related stressors and distress during this transition, focusing on social media activity as a potential moderator. A longitudinal sample of 349 students at an urban university (116 men, 222 women, 11 nonbinary; Mage = 20.37) completed consecutive waves of measures (fall 2021 to spring 2022). A cross-sectional replication was recruited in spring 2022 (163 men, 229 women, 34 nonbinary). In both samples, we assessed social media activity using a newly developed measure. We also assessed internalizing symptoms, loneliness, and exposure to pandemic stressors. COVID-19 stress predicted increases in internalizing symptoms, but the effect held only for students who acknowledged high levels of active online communication. •COVID stress was associated with internalizing symptoms for undergraduates returning to campus after remote instruction.•Active and passive subtypes of social media use were demonstrated in two independent samples.•Online-only communication and active communication moderated associations between COVID stress and internalizing symptoms.•Links between COVID stress and internalizing held only at high levels of online-only communication or active communication.