The main goal of this article is to analyze the association between the usage of internet social networks (in the example of Facebook) and the participatory dimensions of social capital of youth in Croatia. The research used Robert D. Putnam's operationalized participatory dimensions of social capital as well as theories of internet social networks as potential agents of social capital. The research was conducted via online survey in 2012 on a convenience sample of Croatian youth (N = 577). The results indicate there is a consistent link between the usage of internet social networks and the number of memberships in non-governmental organizations and civil activism. A positive correlation with activism remains significant even after including standard correlates such as memberships in organizations or generalized trust. Religiosity is positively associated with membership in non-governmental organizations, but negatively with social engagement and activism. It is concluded that internet social networks, due to their technological and communication characteristics, serve as a relevant agent for participatory practices of youth with the necessity to expand research with a probabilistic sample.