This study was designed to examine the effects of playing the online game World of Warcraft (WoW) on adolescents' social competence and loneliness, and to investigate the underlying mechanisms of the Internet-affected social compensation hypothesis. The hypothesis states that being online affects adolescents' social competence as a result of a variety of communication partners and identity experiments online. A survey was conducted among 790 high school students. There appeared to be no direct effect between playing WoW and adolescents' social competence and loneliness. We did find an indirect effect via variety of communication partners. Adolescents who play WoW vary more in their communication partners, leading to an increase of social competence and a decrease of loneliness.