This paper reports on a study on the use of social network sites (SNSs) designed for L2 learning, such as "Livemocha" and "Busuu", where learners autonomously seek opportunities for authentic interaction in spontaneous ways. The study consists in a longitudinal multiple case study approach to investigate learners' informal online interactions taking place in the SNSs. This paper will focus on the results related to the analysis of learners' interactions and to whether the construction of learning opportunities is fostered or impeded by the social dimension that is intrinsic in these communities. The objectives are to learn more about the dynamics and the behaviours enacted by learners with reference to the online interaction with peers, and to explore the role played by the social aspect and its relationship with the learning aspect. To attain these objectives, the paper analyses intercultural, open-ended, dyadic conversations occurring between learners and native speakers (NSs), and learners and non-native speakers (NNSs) in the semi-instructional context of these learning communities and in the absence of teachers and pedagogical tasks. Drawing on socio-cultural approaches, the paper also raises central issues that are related to the surrounding environment of online language learners, such as roles' definition, learners' identity, scaffolding and peer-assistance (macro-level). It then applies these issues to key-concepts in SLA, such as turn-taking, language selection, language alternation, repair strategies and noticing (micro-level). The data collection includes semi-structured interaction interviews and a wide and variegated corpus data consisting of textual private messages and emails, audio and video recordings and textual chats analysed respectively through virtual ethnography and Conversation Analysis (CA). The preliminary results provide insights on learners' ability or inability to manage both the social and the pedagogical trajectories simultaneously. These deliveries are expected to shed more light on their interaction patterns and to provide a better understanding of recent lifelong L2 learning practices in the naturalistic and out-of-class contexts of online communities. [For the complete volume, see ED574893.]