We proposed a multilevel model of structural influences on HIV-risky sexual partnerships in a diverse sample of 1793 youth residing in 23 states and the District of Columbia. We examined the influence of concentrated disadvantage, HIV stigma, and sexual and gender minority stigma on engagement in HIV risky sexual partnerships and whether youth's participation in opportunity structures, anticipation of HIV stigma, and perceptions of their community as youth-supportive settings mediated structural effects. After controlling for age, HIV status, and race, we found structural HIV stigma had deleterious indirect effects on youth's participation in HIV-risky sexual partnerships. Concentrated disadvantage and structural sexual and gender minority stigma had direct negative effects on youth's perceptions of their communities as supportive and on their participation in prosocial activity. Support perceptions had direct, protective effects on avoidance of HIV-risky sexual partnerships. Structural stigma undermines youth's belief that their communities invest in their safety and well-being.