Evidence has shown that social anxiety significantly influences internet addiction among adolescent students. However, the boundary conditions that strengthen or weaken this association with internet addiction have not been fully understood, especially in sub-Saharan Africa. This study adopted a cross-sectional survey design to investigate the direct effect of social anxiety on internet addiction among adolescent students and the moderating role of family functioning in such relationships. A sample of (N = 1800) students (age range 11-17 years; M = 15.30 years; SD = 1.99) from 10 secondary schools in Southeast Nigeria participated in this study. The participants completed the self-report measures of the Social Phobia Inventory, Family APGAR (adaptability, partnership, growth, affection, and resolve) Index, and Internet Addiction Test. Pearson correlation was used to determine the bivariate relationship among the study variables, while Hayes regression-based PROCESS macro was used for moderation analysis. Findings revealed that social anxiety was positively associated with internet addiction. Family functioning was negatively associated with internet addiction. Family functioning did not moderate the relationship between social anxiety and internet addiction. We concluded that reducing social anxiety and bolstering family functioning may be an effective strategy to lessen the vulnerability of adolescents to internet addiction.