Concerns about mental health difficulties in young people, mid-adolescent girls in particular, are on the rise. Many explanations ranging from peer pressure and bullying, to social media and gender inequality, have been offered for the rise in mental health problems. This study utilised data from the Millennium Cohort Study (Wave 6) to examine 14-year-olds' mental health and wellbeing in relation to familial and peer interactions, gender, socio-economic factors and social media use. Across measures of mental health and wellbeing, the findings showed that girls fared much worse than boys, particularly in experiencing negative feelings and low self-concept and life satisfaction and in self-harming. Teenage girls appeared to have become the new 'high risk' group. The findings from this study have implications for young people's mental health and wellbeing especially as seen through the lens of income and gender inequality. Given the current political concerns about young people's mental health, this study is hoped to contribute to an informed debate about individual wellbeing within a broader social milieu.