<p>Shyness is a major risk factor for the incidence of problematic social media use (PSMU) in adolescents, yet few studies have explored the potential mediating and moderating mechanisms linking shyness to PSMU. This study used a cross-sectional design to investigate the mediating roles of peer victimization and online upward social comparison, as well as the moderating role of psychological resilience. A total of 1506 Chinese adolescents (<i>M</i>_<i>age</i> = 13.74, <i>SD</i> = 0.98) completed self-report questionnaires measuring shyness, peer victimization, online upward social comparison, psychological resilience, and PSMU. After controlling for the effects of age, gender, and family economic status, results revealed that adolescents higher in shyness were more prone to suffer peer victimization and make online upward social comparisons, and both factors subsequently predicted a greater occurrence of PSMU. Furthermore, psychological resilience moderates the second half of two mediating pathways. Specifically, compared to adolescents with low psychological resilience, those with high psychological resilience exhibited a weaker positive relationship between online upward social comparison and PSMU, and a stronger positive relationship between peer victimization and PSMU. These findings enhanced the current understanding of the mediating and moderating mechanisms associating shyness with PSMU among adolescents, indicating that targeted intervention measures can effectively reduce the level of adolescents’ PSMU.</p>