The literature on students' perceptions towards using Social Media (SM) for language learning reports mixed findings: while some studies indicate learners' positive perceptions of their use for academic purposes (e.g., Bani-Hani et al.), others suggest that learners' perceptions might vary due to their proficiency in the language (e.g., Gamble & Wilkins). There is also evidence that students' do not always wish to share their SM environments for educational purposes). This study investigates students' attitudes towards the use of four popular SMs (WhatsApp, Snapchat, Instagram and Twitter) in learning English as a foreign language. Ninety-nine adult English learners at a university in Saudi Arabia, active users of SM, participated in this mixed-methods study, which consisted of individual surveys and interviews. A two-way analysis of variance revealed that there are differences between beginner and advanced students in their perceptions of the usefulness of SM applications for language learning, but not in their affective feelings towards SM use outside the classroom, nor their choice of SM application for learning. Frequency counts indicated that the groups' choices of SM varied according to different language purposes and the skills to be learned (e.g., they preferred WhatsApp for communication with family and friends, Twitter for reading, and Snapchat for learning aural skills). Further qualitative analysis revealed that advanced learners were more reluctant to using SM for academic purposes.