Young people are increasingly turning to social media for health-related information in areas such as physical activity, diet/nutrition and body image. Yet, there are few robust empirical accounts of the content and form of the health-related material young people access and attend to, or the health-related content they create and share. Furthermore, there is little guidance from research or policy on young people's engagement with health-related social media. This leaves many relevant adults ill-equipped to protect young people from the negative influences of social media and to optimize the potential of social media as a medium for health promotion. This article presents new evidence on young people's engagement with social media and the influences they report on their health-related behaviors. The research was undertaken with 1296 young people (age 13-18) using a participatory mixed methods design. Initially, a public pedagogy [Giroux, 2004. Public pedagogy and the politics of neo-liberalism: Making the political more pedagogical. "Policy Futures in Education," 2, 494-503] theoretical framework was used to guide data analysis but this was found to be limiting. An adapted framework was developed, therefore, drawing on Miller et al. [2016. "How the world changed social media." London: UCL Press] and Lomborg [2011. Social media as communicative genres. "Journal of Media and Communication Research," 51, 55-71] to account for the unique ways in which pedagogy operates in a social media context. Young people accessed and used a range of health-related information on body transformations, diet/nutritional supplements or recipes and workouts/exercises, albeit in different ways. Moreover, young people identified five forms of content that influenced their understandings and behaviours: (i) automatically sourced content; (ii) suggested or recommended content; (iii) peer content; (iv) likes; (v) reputable content. The findings also suggest that relevant adults can reduce risk and realize more of the positive impacts of social media for young people by focusing on content, and the ways in which content is shaped in the interplay between interactive functionalities of social media (e.g. likes and followers) and young people's social uses of social media (e.g. friends, information).