This paper, drawing upon a mobile telecollaborative project, resonates with the rapid development of technology in language learning. We employed the instant messaging app WeChat to create an English telecollaborative environment for two groups of Chinese students to communicate within. Interview data were triangulated with students' chat transcripts and comments from a teacher's reflective journal. A mixed-methods approach, including quantitative descriptive analysis, thematic analysis and content analysis, was used to investigate the challenges and the linguistic performance by applying the community of inquiry framework to the students' chats. The analysis illustrates some of the complexities and challenges of using online apps as a way of communicating in a second language: students expected more teacher support, they struggled to use the app due to their physical environments and they felt that they were not sufficiently well prepared for chatting in an English medium environment. Based on the findings, a conceptual model is proposed for consideration when encouraging students to engage in telecollaborative learning.