Transitioning from school to university is a major development for learners, often accompanied by difficulties. When overseas students arrive at university for the first time these challenges are multiplied. It is suggested, however, that these difficulties can be mitigated to a certain extent via the use of online social networks. The present study, using data generated by a group of 350 first-year students from mainland China (called QQ), explores how an online instant messaging service helped the students adapt to life in a Hong Kong university. Findings reveal that (a) first-year mainland students experienced specific problems at distinct stages; (b) the QQ provided informational, instrumental and emotional support for the students; (c) the QQ was self-emergent and had a clear annual cycle. It is argued that self-initiated peer support among students plays a vital role in higher education, especially at crucial periods such as school-to-university and cross-border transitions.