Social media addiction (SMA) and social phobia (SP) are significant adolescent mental health concerns. In Saudi Arabia, despite high social media penetration, the specific association between these two constructs remains under-researched, particularly in the Aseer region. This cross-sectional study aimed to examine this relationship, conducted from January–March 2025, recruiting 384 Saudi adolescents (aged 11–19) from schools using a multistage cluster sampling strategy. Participants completed validated self-report measures, including the Social Phobia Inventory (SPIN) and the Al-Menayes Social Media Addiction Scale. The prevalence of moderate-to-severe social phobia was 15.3%. A significant, moderate positive correlation emerged between SP and SMA scores (Spearman’s rho = 0.294, p < .001). After adjusting for age, gender, and family income, adolescents with moderate social phobia had 2.17 times the odds of probable SMA compared to those with no social anxiety (Odds Ratio [OR] = 2.17; 95% CI [1.03–4.59]; p = .043). Social phobia and social media addiction are significantly intertwined public health challenges among Saudi adolescents in the Aseer region. These findings support the urgent need for integrated mental health and digital literacy interventions that proactively screen for both conditions.