One of the most studied variables in virtual online education is engagement because it contributes to retention and academic performance. Several studies show that the didactic design of the virtual course, the role of the teacher, interactivity, interaction, time spent in the virtual environment, and the use of digital social networks increase engagement. However, there is a lack of research that compares which of the two digital social networks, WhatsApp or Telegram, promotes higher levels of engagement. This study’s objective is to analyze the effect of the educational use of Telegram on student engagement. An experiment (pretest and posttest with a control group) is designed using a mixed-methods approach based on a convergent or concurrent triangulation design. The study populations (coincides with the sample) are those enrolled (n = 229) in the six editions of a virtual postgraduate course. The techniques used for data analysis were scatter plots, content analysis of teachers’ narratives, and statistical methods. The triangulation of the quantitative and qualitative results confirms that the educational use of digital social networks promotes engagement in all experimental groups (use of the virtual learning environment and Telegram) obtaining greater significant differences than in the control groups. It is concluded that the use of the following Telegram functionalities, chat groups, peer assessments, support for various types of online interaction, the exchange of digital media, and the design of surveys contributed, under the guidance of teachers, is to increase the student’s engagement.