During the COVID-19 pandemic, young people have become overexposed to social media and online gaming, making them more vulnerable to online violence such as cyberbullying. The aim of this study was to determine whether social media and online gaming pose a risk for cyberbullying through time spent online and whether there is a sex that is more vulnerable to this phenomenon. The survey included a sample of 4338 students (52.4% girls; age range, 11–19 years, M 14.1 SD 1.6) attending lower and upper secondary schools. Multiple moderated mediation regression models by sex were conducted, showing a relationship between social media and online gaming, time spent online outside of school, and cyberbullying. The results show that young girls are at higher risk of cyberbullying via social media, and boys are at higher risk of cybervictimization through online gaming. The findings may encourage other researchers to study the phenomenon, taking into account the role of parents and other educators.