How does the use of social networking sites (SNSs) affect social capital offline and online? The increasing popularity of SNSs such as Facebook (FB) implies a significant change in the way we interact with others. In an extensive longitudinal study (N = 311), carried out in Norway between 2008 - 2010, we examined the relationship between FB use and social capital, with a focus on interpersonal interaction, including face-to-face (F2F) interaction. Our findings suggest that overall FB use does not significantly affect offline capital, despite a significant increase in the use of FB from 2008 to 2010, after controlling for age, gender and education. However, different types of communication strategies on FB correlate with various kinds of F2F interaction. Importantly, FB users who focus on FB communication with their close friends, also interact more frequently with their close friends F2F, compared to those using FB to communicate with "online strangers”. The results also indicate that FB has become an important tool for keeping in touch with family members and existing friends rather than forming new connections.