During the past few years, hundreds of thousands of Danes have created personal profiles on websites such as Arto, Facebook and MySpace. With the emergence and popularisation of these sites, we have witnessed a new media concept: social network(ing) sites. As is often the case with new media, teenagers have been the first to take social network sites to heart. In this paper I discuss the concept of online social networking and describe how social network sites are used as part of everyday teenage life to maintain social relations. I do this, firstly, by presenting a number of concepts that I consider to be important in relation to young people's use of social network sites. Secondly, I highlight some results from my own research on 12-18-year-old children and adolescents’ use of various social network sites, including Arto.com, which has been Danish teenagers’ preferred venue on the Internet for a relatively long time. Using empirical examples, I analyse and discuss how social network sites are an integral part of the young users' friendships and social lives. The article is based on four years of ethnographic studies.