The study sought to assess students' use of social media and its effect on academic performance of tertiary institutions students in Ghana with a focus on Koforidua Polytechnic students. Questionnaire was used for collecting data. Out of one thousand five hundred and seventy-eight copies of the questionnaire distributed, one thousand five hundred and eight were retrieved which represented a response rate of 95.5%. The study revealed that majority of the respondents had mobile phones which also had Internet facility on them and had knowledge of the existence of many media sites. The study further confirmed that most of the respondents visit their social media sites using their phones and spend between thirty minutes to three hours per day. In addition the study revealed that the use of social media sites had affected academic performance of the respondents negatively and that there was direct relationship between the use of social media sites and academic performance. The study recommends among others that, students with mobile phones having internet facility should be encouraged to use it to supplement their research in the library rather than the usual charting with friends all the time. Students should be encouraged to limit the time they spend on their social media sites per day and advise them to rather substitute those hours to read novels to improve their knowledge. Since the use of social media sites had affected the academic work of students negatively there is the urgent need for the introduction of students to the availability of novels and other information resources or materials that can help them academically.