We assessed the relationships among HIV-related social and behavioral outcomes resulting from an adolescent-focused HIV structural change initiative in eight urban sites operating Connect to Protect (C2P) coalitions. Over a 4-year period, annual cross-sectional panels of adolescents (N = 2,248) completed an audio-computer-assisted interview, providing data on satisfaction with their communities as adolescent-supportive environments, internalized HIV stigma, lifetime HIV-testing, lifetime sexual risk-taking, and number of sexual partners in the prior year. We used structural equation modeling to estimate hypothesized links between time since coalition mobilization to our social and behavioral outcomes. Over the 4 years, adolescents perceived their communities to become more supportive (p < .05). Positive perceptions of community support were associated with lower lifetime HIV sexual risk (p < .05). The effect of time on risk behavior was mediated by perceptions of community support. Stigma was unchanged over time. Stigma had damaging effects on risk behavior, effects which were also mediated by perceptions of community support. Special efforts are needed to address the deleterious effect of HIV stigma on high-risk urban adolescents.