In this study, we assess the potential significance of two broad categories of online activity: friendship-driven (FD) and interest-driven (ID) engagement (see Ito et al., 2009; Jenkins, 2009). We test the hypotheses that these practices will create on-ramps to political activity, both online and offline, by fostering politically relevant skills and online social networks that prompt exposure to political issues. Our analyses employ a cross-lagged model, drawing on data from the 2013 and 2015 waves of the Youth Participatory Politics (YPP) Survey, a nationally representative panel of youth who were 15–27 years of age in 2013. Our findings illustrate the importance of FD and ID online activity for the development of youth political engagement, both online and offline. In addition, they highlight the importance of online social networks as a mechanism for leveraging weak social ties that promote participation.