Although part of their use is intended for leisure, social networks could be a useful tool for developing students' critical thinking. Nevertheless, this relationship could also be influenced by our competence in learning to learn, that is to say, our knowledge, skills, and attitudes associated with self-regulation, metacognition, use of learning strategies, and problem-solving. To test this hypothesis, 301 university students participated (M = 19.83; SD = 3.17). The results showed which functions of social media related to information, content creation, and problem-solving were associated with a higher level of Learning to Learn competence and of Critical Thinking. However, the different functions of social media use were poor predictors of Critical Thinking, with the best predictor of critical thinking being the competence of learning to learn. Finally, in students with a low competence in learning to learn, a greater interaction with their immediate environment (e.g. friends, family…) or with their teachers or peers through social media was associated with a higher development of critical thinking. Moreover, in students with a high competence in learning to learn, a greater use of social media to solve academic problems was associated with a higher development of critical thinking. These results shed some light on the potential benefits that the use of social media could bring in both formal and informal settings, as well as the need to work among university students on some of the main aspects of the learning to learn competence, like metacognition, self-regulation or problem-solving, to develop critical thinking.