Non-suicidal self-injury (NSSI) is of increasing concern, yet many adolescents who self-injure are reluctant to seek professional help. Instead, they turn to friends for support, although it is unclear what these friends can offer. This study aimed to identify adolescents' views of how peers and online friends can help young people who self-injure, and examine differences according to age, gender, and exposure to NSSI. Students (n = 2,637; aged 12-18 years) from 41 schools completed questions asking them to describe what peers and online friends could do to help young people who self-injure. Thematic analysis identified seven strategies, including communication about NSSI with peers and online friends, referral to adults and health professionals, greater public awareness of NSSI, and reduced peer stigma and bullying. Endorsement of themes varied by age, gender, and experience with NSSI. Findings have implications for school prevention of NSSI.