Abstract Adolescents vary widely in how they engage with digital media, yet prior research often overlooks the heterogeneity and developmental dynamics underlying these behaviors. Using four waves of data collected between 2013 and 2021 from a nationally representative sample of U.S. adolescents (N = 14,798; ages 12–17 at baseline), we identified three media use trajectories via latent class growth analysis: low‐increasing, moderate‐stable, and high‐stable. Internalizing and externalizing problems significantly predicted trajectory membership. To examine bidirectional associations between media use and psychological symptoms, we applied autoregressive latent trajectory cross‐lagged panel models, which allowed for the modeling of within‐person dynamics while accounting for interindividual change patterns. Results revealed several modest but significant bidirectional effects between media use and psychological problems over time. Specifically, higher media use predicted later increases in externalizing and internalizing symptoms, while earlier media use was also associated with short‐term reductions in internalizing problems. Strong trait‐level associations were observed across all three constructs, indicating that adolescents with consistently high media use also experienced persistent emotional and behavioral difficulties. These findings highlight the heterogeneous and dynamic nature of adolescent digital engagement and its mental health correlates. The results underscore the importance of person‐centered and developmentally informed interventions that account for psychological vulnerability and sociodemographic context.