The younger generationās widespread use of online social network sites has raised concerns and debates about social network sitesā influence on this generationās civic engagement, whether these sites undermine or promote prosocial behaviors. This study empirically examines how millennialsā social network site usage relates to volunteering, using the 2013 data of the Minnesota Adolescent Community Cohort Study. The findings reveal a positive association between a moderate level of Facebook use and volunteering, although heavy users are not more likely to volunteer than nonusers. This bell-shaped relationship between Facebook use and volunteering contrasts with the direct correlation between participation in off-line associational activities and volunteering. Overall, the findings suggest that it is natural to get mixed messages about social network sitesā impacts on civic engagement, and these platforms can be useful tools for getting the word out and recruiting episodic volunteers.