Language Learning Social Network Sites (LLSNSs) have attracted millions of users around the world. However, little is known about how people participate in these sites and what they learn from them. This study investigated learners' attitudes, usage, and progress in a major LLSNS through a survey of 4,174 as well as 20 individual case studies. The study hints at the potential of LLSNSs, given the generally positive regard participants have for the site, but it also shows its limitations, since most learners drop out or show only limited gains. The study suggests that if online education is to play a positive role in the teaching and learning of English and other languages, learners will need support, guidance, and well-structured activities to ensure the kinds of participation and linguistic interaction that can lead to success.