This article focuses on the role that metacognition can effectively play in the development of second language listening comprehension, and specifically, how a mobile app can be specified to this end. A social mobile assisted listening app, ANT (Audio News Trainer), is presented as a prototype for exploring the way in which students can be helped to use metacognition to improve relevant linguistic communicative competences. A study has been undertaken with students using ANT to explore the intricate nature of the listening comprehension development process and the main metacognitive strategies that can be successfully applied. Special attention is paid to the implicitly and explicitly applied metacognitive strategies within the app, and related social network, where follow-on activities were undertaken, the strategies in question being: focus (a conscious effort on the gradual development of individual skills), engagement (interest is enhanced when a learning activity is enjoyable/successful), interaction (since collective activities seem to enhance emotional and social involvement), reflection (upon what works and does not work for each individual), self-regulation (through data about the students' own progress and achievements), and attitude (here a further distinction is made between satisfaction, self-confidence and encouragement). The stages of engagement of a student with the app are explored in relation to the metacognitive strategy used and how they can contribute to the overall success of the learning experience. Finally, a reflection is made about how metacognitive strategies offer an effective way to compensate for the lack of teacher presence, support and guidance, on a medium/long term basis. However, although the study of the initial use of this social listening training app shows the potential for incorporating 'knowing about knowing' into mobile technology, it is suggested that future research is required to provide finer-grained insights into this process.