Research on participation of social media users has contributed to our understanding of modern citizenship, civic engagement, and contemporary public sphere. Despite a growing interest in participatory practices in social media little is known about the factors affecting political participation of social media users. Based on an online survey of 700 social media users in Poland, this study examines the relationship between social capital (defined at the individual level as a resource embedded in personal networks) and political participation. It has been established that there is a contradictory relationship between social capital and participatory activities of social media users. Apparently, differences between the resources that are only embedded in personal networks on the one hand, and those that can be mobilized for purposive actions on the other, matter when association between social capital and political participation is considered. Moreover, the presence of these resources significantly varies across different types of social relations (family, friends and acquaintances) of respondents engaged in different participatory actions.