Introduction: The 15-20% of adolescents worldwide who engage in non-suicidal self-injury (NSSI) face an increased risk of transitioning from suicidal ideation to suicide attempt. To resist NSSI urges, young people often seek peer support online. We examined adolescent help-seeking on a purpose-built online mental health peer support platform, which is a critically understudied help-seeking venue.Methods: Adolescents’ help-seeking posts in the “Self Harm” category on a large online peer support platform (575,261 posts from 114,937 users) were analyzed using topic modeling. We assessed the prevalence of NSSI-related topics versus morbid/suicidal topics.Results: Our 12-topic model produced interpretable themes. Three main findings emerged: posts included little information about the context of self-harm behavior; there was minimal evidence of pro-self-harm content in posts; and the primary topics of the posts were evenly split between NSSI-related topics and morbid/suicidal topics.Conclusion: Our findings have important implications for online mental health communities: requiring users to select a narrow category for their post may limit contextual information; moderation of pro-self-harm content may reduce its prevalence; and the absence of dedicated spaces for suicidal users may funnel those users into NSSI-focused spaces, potentially increasing risk for all users.