With the recent COVID-19 pandemic and disruption of campus-based education, the use of mobile social networking applications to supplement formal education has attracted a great deal of attention. Teachers do have opportunities to join students' online groups to share, clarify, and exchange housekeeping information and course-related content with them. Teachers can, in particular, provide English as a foreign language (EFL) students with more sources of linguistic input, interaction, and feedback. Research investigating this potential, however, is still scarce in such contexts. The current study explores the likely affordances of teaching presence in students' WhatsApp groups for designing, facilitating, and guiding cognitive and social processes conducive to their language learning. A mixed-method design was employed to collect both quantitative and qualitative data and information from English-major undergraduates (N = 111) and faculty teachers (N = 8) who joined the same WhatsApp groups for one academic semester at a major university in Oman. Descriptive and thematic analyses of data from a survey with both closed-ended and open-ended questions and semi-structured interviews indicate that the shared WhatsApp groups functioned as small close-knit communities where students were able to constantly access teachers for their assistance, feedback, and clarification of content. Despite these merits, however, the participating faculty believed that the presence of teachers in WhatsApp groups might have consequences for students' tolerance of ambiguity, scaffolding, and autonomous language learning. The paper concludes by discussing several pedagogical implications and directions for future research.