In the last of few years, the use of social media has become the main topic in teaching and learning, but by the rapid development of technology, there must be a shift of students’ interest in employment the media. Thus, this research aimed to reveal; (1) Do the use of social media improve the EFL students’ writing skill; and (2) What factors affect the EFL students’ writing achievement. This research employed experimental design. The respondent of the current research were two classes of third semester EFL students at the University of Jember. In collecting data, the researchers used writing test, interview, and observation. The data were analyzed using SPSS 18.0. The researchers found that; 1) The use of social media did not significantly improve the students’ writing skill, and 2) There were some specific factors that hindered the students; achievement in writing descriptive text.