This mixed-methods study examines high school students' self-confidence, social media use, and internet addiction. The data were collected from 340 high school students in Samsun during the 2019-2020 academic year. Participants completed self-confidence, internet addiction, and social media use scales, and interviews. Descriptive analyses, t-tests, ANOVA, and Pearson correlation tests were used. Results showed that self-confidence levels varied among participants, and 6.5% of participants were addicted to the Internet. Self-confidence levels were higher among 9th-grade students, while social media use differed significantly among 11th-grade students. No significant differences were found by gender. Internet addiction increased as social media use and self-confidence levels decreased. Qualitative findings revealed that participants use the internet and social media for various purposes, and some struggle to control their internet use. These results suggest that social media use, self-confidence levels, and age predict internet addiction. Future studies could explore these variables in more detail.