This study focuses on the role of online civic participation in the civic development of adolescents. We build on the assumption that online civic participation differs from more traditional offline civic participation in several key characteristics, namely lacking proximity to other actors, possible disconnection between civic actions and their outcomes, and a reduced hierarchy within the online environment. Considering these specifics, the study examined the longitudinal effect of online participation on the development of civic identity, political self-efficacy, and attitudes toward social authorities. Concurrently, we contrasted the impact of online participation with the impact of offline civic participation. Data from a survey-based two-wave panel study conducted in Spring 2014 and Autumn 2015 in the Czech Republic were utilized. The sample comprised 768 adolescents (aged 14-17 in T1; 54% females). The results showed that online participation predicted increased challenging attitudes towards social authorities, while offline participation had the opposite effect. Furthermore, online participation had no effect on political self-efficacy or civic development, but offline participation positively predicted civic identity. The findings are discussed with regard to the specific benefits and limits of online civic participation.