Due to COVID-19 pandemic, schools all over the world have gone from full face-to-face to online lessons. This paper analyzed the influences of social networking sites (SNS) on secondary school students' academic achievement. The original studies were extracted from the Web of Science database, and the review of the 27 selected journal articles revealed that the use of SNS is both positively and negatively related to secondary school students' academic achievement. However, it was found that few studies have reported the positive impacts of SNS use on students' academic achievement. On the contrary, several studies have shown that excessive usage of SNS, inappropriate SNS use, and usage of SNS for other recreational activities instead of educational purposes harmed students' academic achievement. Factors that mediate (such as internet addiction, intention to cyberbully, and sexually explicit material use) and moderate (such as gender, sleep time, learning environment, time management skill and school day and non-school day behaviors) the SNS-academic achievement link are discussed. These findings have important implications for parents, teachers, educationalists, and counselors who should be aware of the potential for inappropriate and excessive use of SNS by students, and who should develop intervention mechanisms to address the problem.