Hispanic/Latino youth are disproportionately affected by obesity. However, how social factors outside of the family relate to Hispanic/Latino youth obesity is not well understood. We examined associations of extra-familial social factors with overweight/obesity prevalence, and their variation by sex and age, in 1444 Study of Latino Youth participants [48.6% female; 43.4% children (8-11 years); 56.6% adolescents (12-16 years)], who were offspring of the Hispanic Community Health Study/Study of Latinos participants. Youth self-reported general social support from friends, dietary-, and physical activity (PA)-specific support from peers, and awareness/internalization of thinness ideals. Overweight/obesity was defined as body mass index ≥ 85th percentile. Logistic regression models assessed effects of social factors and their interactions with age-group and sex, adjusting for potential confounders. Social support from friends interacted with both age and sex in relation to overweight/obesity. Female children who reported lesser (OR 0.60; 95% CI [0.39, 0.91]) and female adolescents who reported greater (OR 1.35; 95% CI [1.06, 1.74]) social support from friends had higher odds of overweight/obesity. Among males, greater awareness/internalization of thinness ideals related to higher odds of overweight/obesity (OR 2.30; 95% CI [1.59, 3.31]). Awareness/internalization of thinness ideals was not associated with overweight/obesity among females. Dietary and PA-specific peer support did not relate to overweight/obesity. Social support from friends and awareness/internalization of thinness ideals were significantly related to odds of overweight/obesity in Hispanic/Latino youth; associations varied by age and sex, and persisted after control for intra-familial factors (overall family support/function; diet and activity specific support).