Social capital among close friends is the norms of trust and reciprocity shared by a group of friends within multistranded networks. This research investigated the factors that contribute to the levels of friendship social capital. It also analyzed whether friendship social capital was associated with participation in voluntary associations and whether those who reported high levels of social capital with their friends also reported higher levels of generalized trust in the wider society. Through an online survey of young Australian residents aged 16 to 25 (N=283) closed networks were found to be associated with very high levels of social capital among friends. Further, those with very high levels of friendship social capital were more likely to participate in organized groups and to report high levels of generalized social capital than those with lower levels of friendship social capital. Thus, promoting friendship networks of young people could benefit society more broadly by fostering participation in voluntary activities and generalized social capital.