Background <p>This study aimed to examine the association between social media content production and adolescent physical health promotion, as well as the potential mediating and sequential mediating roles of online social support and positive psychological capital.</p> Methods <p>A cross-sectional survey was conducted using self-report questionnaires from 3,442 adolescents recruited through a multi-stage sampling procedure across seven major geographic regions in China. Structural equation modeling and bootstrap analysis (5,000 resamples, 95% confidence intervals) were performed.</p> Results <p>Social media content production, online social support, and positive psychological capital were all significantly and positively associated with adolescent physical health promotion. Online social support and positive psychological capital showed independent and sequential mediating roles. The indirect associations via online social support (<i>β</i> = 0.231, 95% CI [0.204, 0.263]), positive psychological capital (<i>β</i> = 0.117, 95% CI [0.090, 0.145]), and their sequential association (<i>β</i> = 0.101, 95% CI [0.084, 0.118]) were all statistically significant.</p> Conclusion <p>This study indicates that social media content production is associated with adolescent physical health promotion through psychosocial factors. However, causal inference cannot be established due to the cross-sectional design. It provides a theoretical basis and practical implications for understanding the psychological and social determinants of adolescent health behaviors and for effectively leveraging social media to support adolescent physical health promotion in the digital era.</p>