Is there a trade-off between having large networks of social connections on social networking sites such as Facebook and the development of intimacy and social support among today's generation of emerging adults? To understand the socialization context of Facebook during the transition to adulthood, an online survey was distributed to college students at a large urban university; participants answered questions about their relationships by systematically sampling their Facebook contacts while viewing their Facebook profiles online. Results confirmed that Facebook facilitates expansive social networks that grow disproportionately through distant kinds of relationship (acquaintances and activity connections), while also expanding the number of close relationships and stranger relationships, albeit at slower rates. Those with larger networks estimated that larger numbers of contacts in their networks were observing their status updates, a form of public communication to one's entire contact list. The major function of status updates was emotional disclosure, the key feature of intimacy. This finding indicates the transformation of the nature of intimacy in the environment of a social network site. In addition, larger networks and larger estimated audiences predicted higher levels of life satisfaction and perceived social support on Facebook. These findings emphasize the psychological importance of audience in the Facebook environment. Findings also suggest that social networking sites help youth to satisfy enduring human psychosocial needs for permanent relations in a geographically mobile world--college students with higher proportions of maintained contacts from the past (primarily high school friends) perceived Facebook as a more useful tool for procuring social support. (Contains 9 tables and 1 figure.)