This chapter focuses on interrogating how screen devices and social media platforms impact adolescent identity formation, with particular focus on teenage girls. As adolescents navigate the challenging physiological and psychological changes of puberty, the chapter posits that social media has created unprecedented avenues for identity exploration that often prove harmful. It also highlights how adolescent girls, already prone to negative emotions and body image concerns during puberty, now face additional pressures through constant social comparison with idealised online personas. This has contributed to alarming increases in mental health issues including anxiety, depression and self-harm behaviours. The chapter identifies concerning trends, including a dramatic rise in gender dysphoria among adolescent girls, suggesting social contagion facilitated by online communities as a contributor to such phenomenon. Through examining historical and contemporary examples of social contagion, the information presented in the chapter illustrates how social media has amplified the spread of harmful behaviours by allowing impressionable adolescents continuous access to damaging ideas and influences without appropriate guidance.