With increasing popularity of social network sites as applications to communicate among adolescents, the Internet has become an important social context for their development. The aim of this study was to examine the relation of the online activities of adolescents (frequency of use and negative experiences on social networks) and their well-being measured by the severity of depressive symptoms, so as theunderlying mechanisms of their relationship; envy and social comparisons and feedback seeking in the context of normative educatioaln and life transition in which they are located. The study included 281 high school students (174 girls) 1st and 2nd grade students from 5 schools in Rijeka (Salesian Classical Gymnasium, Gymnasium Andrija Mohorovičić, School of Medicine, Electroindustrial and trade schools, Mechanical Engineering and Shipbuilding school), the average age of 15.76 years. They were administered the following questionnaires: Scale of envy, Scale of social comparisons and feedback seeking, Scale of negative experiences on social networks and Scale of depression, anxiety and stress. The research results show that girls more often use social networks, have higher levels of envy, social comparisons and feedback seeking and more pronounced symptoms of depression than young men, while there were no differences in sex with regard to the frequency of negative experiences on social networks. The frequency of use and negative experiences on social network sites positively and directly predict severity of depressive symptoms, with significant mediators in the relationship between frequency of use of social networks and severity of depressive symptoms; the feeling of envy and social comparisons and feedback seeking. Despite certain limitations, this investigation confirmed the general assumptions about gender differences in depression, the roles of the frequency of use and the negative experiences on social networks on the severity of depressive symptoms and mediation roles of envy and social comparisons and feedback seeking in the severity of depressive symptoms among adolescents in the normative life and educational transition from primary to secondary school.