In the digital age, social media has become an integral part of university life, influencing students' academic performance and social engagement. This study investigates the relationships between social networking site (SNS) usage, social engagement, self-regulation, and academic performance among Chinese university students. Utilizing a sample of 438 students from a public university, data were collected through a structured questionnaire administered via WeChat and Ding Talk. The analysis employed Partial Least Squares Structural Equation Modeling (PLS-SEM) using SmartPLS version 4.1 to test the proposed hypotheses. The results indicate that SNS usage significantly and positively influences students' academic performance and social engagement. Furthermore, social engagement was found to mediate the relationship between SNS usage and academic performance, suggesting that the benefits of social media extend beyond mere academic collaboration. Additionally, self-regulation was identified as a moderating factor, strengthening the positive impact of SNS usage on academic performance. These findings highlight the importance of leveraging social media as a tool for enhancing academic success while emphasizing the need for self-regulatory skills in navigating digital environments. This study provides valuable insights for educators and policymakers aiming to optimize the academic potential of social media in higher education settings.