Peer groups such as neighbourhoods and hobby circles are important sources of social identity for young people, but their viability is challenged by processes of urbanisation and labour mobility. In recent years, traditional peer groups have been joined by easily accessible computer-mediated groups, which have become an everyday part of life in many countries. In this article, we examine how young people identify with various online and offline peer groups. We compare online and offline identification experiences from the perspective of how socio-demographic position and individual sociability characteristics influence them, and examine how these identification processes differ between national contexts. Empirical analyses are conducted based on a survey of online community users from the UK, Spain and Japan (N=4299). It is found that participants identify as strongly with their online communities as they do with their own families, and stronger than with offline hobby groups. In the mature online societies of the UK and Japan, the online group provides a more socio-demographically inclusive source of identification than traditional leisure-time formations. As friends and family move online, affinity towards online groups is more likely to be a reflection of high sociability than a lack of it. Games, social networking sites and other online environments should be seen as crucial contexts for today's youth's socialisation and identification experiences.