Anxious youth often have trouble regulating negative affect (NA) and tend to over-rely on parents when faced with challenges. It is unclear how social interactions with parents or peers actually helps or hinders anxious youths' success in regulating NA. The aim of this study was to examine whether the success of anxious youths' emotion regulation strategies differed according to social context. We compared the effectiveness of co-ruminating, co-problem solving and co-distracting with parents/peers for regulating anxious youth's NA in response to stress in their daily lives. We also examined the benefit of attempting each strategy socially vs. non-socially (e.g., co-ruminating vs. ruminating). One-hundred-seventeen youth (9-14) with a current diagnosis of Separation Anxiety Disorder, Generalized Anxiety Disorder, and/or Social Phobia completed an ecological momentary assessment (14 calls over 5 days), reporting on recent stressors, their affective state, presence of others, and emotion regulation strategies within the prior hour. Mixed linear models revealed that co-distracting was the most effective social strategy for reducing NA, but only for boys. Co-rumination was the least effective social strategy for regulating NA. Regarding social context, only co-distracting was more effective for regulating NA over distracting alone, but only among anxious boys. Results suggest that co-rumination is an ineffective use of social support for regulating NA. Anxious boys may benefit from social support by co-distracting with parents/peers, but improper use may reflect avoidance and contribute to long-term anxiety maintenance. Results extend research on gender differences in interpersonal relationships and emotion regulation.