Background: Internet use has become widespread among young people, and internet addiction has become one of the most common social problems. Internet addiction of students can change the purpose of social media use and create feelings of loneliness. Aim: In this study, it was aimed to identify the relationship of Internet addiction with social media use purposes and loneliness levels in adolescents. Methods: The analytical cross-sectional type study was conducted with 520 students who agreed to participate in the study and attended the 9th, 10th, 11th, and 12th grades of 6 high schools in the province of Erzincan, Turkey, during the 2017-2018 academic year. The “UCLA Loneliness Scale Short Form,” “Young’s Internet Addiction Test-Short Form,” “Social Media Use Purposes Scale,” and “Question Form” were used in the study. In the analysis of the data, numbers, percentage, minimum and maximum values, mean and standard deviations, the analysis of variance, independent-samples t-test, and correlation analysis were used. Results: A statistically significant, positive, and weak relationship was found between the Young’s Internet Addiction Test-Short Form score and the interaction between individuals sub-scale (r = 0.359, P < .001) and the total score of the Social Media Use Purposes Scale (r = 0.236, P < .001). A statistically significant, positive, and weak relationship was found between the Young’s Internet Addiction Test-Short Form score and the UCLA Loneliness Scale Short Form score (r = 0.181, P < .001). Conclusion: As the Internet addiction increases, the use of social media for interaction between individuals and loneliness also increases. Therefore, information about the Internet use statuses of students should be collected in schools periodically from the students and parents, and awareness of students and parents should be raised regarding the Internet addiction.