In this article we explore young Brazilians’ reinforcement of gender-stereotypical and gender non-conforming expressions on social media, to see how Brazilian teenagers reproduce or contest the hyper-sexualized, heteronormative discourses around femininity and masculinity. Three models inspired the theoretical frameworks, namely the Butlerian discoursive subjectivity and performativity, Karen Barad’s model of posthuman materialism and the concept of intra-action of non-human agents, and Sonia Livingstone’s concept of social media literacy. The sample consists of 12 focus groups (60 respondents, 11 to 17 years old) conducted in metropolitan area of São Paulo in September 2016. Overall, our study showed a reinforcement of the heterosexual matrix, with some notable exceptions of contestation from both boys and girls. Our article offers a contribution to the research on young people and social media in South America through taking into account both local contexts and dominant discourses around gender and sexuality.