The Community of Inquiry (CoI) framework has been widely used in blended and online educational research, more recently being applied also to social media settings. This paper explores the learning community created in such a social media-based educational environment, using an extended version of CoI, which includes four components: cognitive presence, social presence, teaching presence and learning presence. The context of study is a project-based learning scenario implemented in an undergraduate Computer Science course. A quantitative content analysis method is employed, to examine a total of 1712 online contributions (blog posts and tweets), generated by 75 students. Results show that the social media tools provide complementary support to the community of inquiry: the blog is primarily a content space (as cognitive presence is dominant), while Twitter is mostly a discussion space (as social and learning presences are dominant). Teaching presence is barely exhibited by the students, being mainly the preserve of the instructor, while learning presence is quite strong, reflecting students' significant self- and co-regulation behavior.