This qualitative case study explores how a teacher positions himself in a social networking platform to create a learning environment in a secondary school science class in Turkiye. Sixty-six students' and their science teacher's interactions on a social networking platform have been observed for one year and nine months. Online and face-to-face interviews, online participant observation, and documentation were used for data generation during the first nine months. The data was analysed with an inductive thematic approach. The results revealed that the teacher created a sustainable online learning platform through four main communication acts: Initiative, Reflective, Supportive, and Informative. In particular, the teacher's initiative and supportive behaviours in the online platform increased student engagement and created a sense of care. Regarding the student's engagement, the teacher's communicative acts' informal nature is perceived as more important by the students than the type of communication itself. It was underlined that there is a need to redefine middle school teachers' presence in a social media platform where the effectiveness of learning increases if they become an 'insider' rather than an instructor.