In recent years, the huge success of social network sites (SNSs) has principally been determined by their ability to link people and their respective relationships. These relationships allow people to access different resources, information, emotional and social support, entertainment, as well as providing them with the opportunity to extend personal social ties. This paper investigates the way in which SNSs are used by emerging adults, defined as young people in the transition from adolescence to adulthood, and particularly those in their last year of high school or at university. The study focuses on different types of social capital and on the use of SNSs by emerging adults during this transitional phase in maintaining and developing relationships. Data collected from a questionnaire administered to 927 emerging adults show, first of all, the relevance of different types of social capital (bridging, bonding and maintaining) based on the student's position (high school, university first-year student or university student). Second, the data analysis indicates that SNSs can be conceived as part of functional organs that support emerging adults in their ability to connect and to be connected to a social network and to develop and maintain it over time.