This study examines the role of social networking sites on the learning processes, teaching practices and professional development of secondary school teachers. By conducting observations and in-depth interviews with active participants, we present an ethnographic study of the "Facebook" group "Teaching ideas secondary education" [author's translation], which is hosted and primarily employed by Flemish teachers. By drawing parallels between the study findings and the theory of "affinity spaces" we aim to gain greater insight into emerging group dynamics and social informal learning processes. According to respondents, the "Facebook" group has the potential to address teachers' needs with respect to the exchange of teaching ideas, experiences and materials. The findings point to a number of emerging developments in the educational landscape, highlighting that social media environments present a new source of inspiration, and combined with a collaborative atmosphere are able to stimulate cross-fertilization, social informal learning processes and self-management and -reflection. We hold these findings up to the light of current education discourses.