In this position paper, we explore the potential of social networks for teacher professional development. Networking is a crucial skill in professional careers, supporting the individual's personal and professional learning. Collective teacher interactions online can facilitate collaborative professional development and support collective epistemic engagement. Social networks can be considered as 'third spaces' between formal and informal learning to support professional development, also integrating international and intercultural aspects. Research questions addressed here include implications of online engagement on teachers' initial and in-service training and impact of social networks on innovations in professional practices and local communities.