Purpose: Mobile health (mHealth) apps may support improved health behavior practice among youth living in larger bodies. However, long-term use is low, limiting effectiveness. This study evaluated whether youths' motivation, satisfaction, engagement with social features, or parent co-participation supported long-term use of an app named Aim2Be. Methods: A secondary analysis of two versions of Aim2Be (preteen and teen versions) using covariate-adjusted multivariable regression was conducted. We evaluated associations between social support features (a virtual coach, a social poll, or a social wall), parent co-participation (time spent in the parent app), and app satisfaction on use (time spent in Aim2Be). Models were stratified by age and satisfaction was explored as a moderator. Results: Preteens (n = 83) engagement with the social poll (β = 0.26, p < 0.001), virtual health coach (β = 0.24, p = 0.01), app satisfaction (β = 0.31, p = 0.01), and parent co-participation (β = 0.24, p = 0.01) predicted use. In teens (n = 90), engagement with the virtual coach (β = 0.31, p < 0.001) and full utilization of social wall features (β = 0.41, p < 0.001) predicted use. Furthermore, satisfaction moderated the effects of partial utilization of the social wall among teens (β = 0.32 p = 0.02). Conclusion: Social support in mHealth apps may impact users differently depending on age. Features that include health professionals or peers may be more advantageous across ages. App developers should consider age when designing interventions. Clinical Trial Registration NCT03651284.