Using online discussion forums and peer-to peer interactive learning currently becomes a common instructional proposition. Such social discourse is educationally adopted to enhance learning and through ideas interchanged in an online setting. The aim of this study was to investigate the use of LINE as an instructional tool complementing language practice to express opinions in an EFL course. In order to examine factors related to student learning performance in the online discussion activity, data were collected from learning score, quantity of interaction, as well as attitude from 83 students. Frequency, mean, and correlation coefficients were employed to analyze. The findings revealed students’ positive attitude toward the online activity, with the highest mean score indicating an enjoyable learning environment. The students’ learning outcome showed positive correlation with frequency of their interaction; however, it was disassociated with their attitude toward the assigned online task. Furthermore, students’ engagement in the learning disclosed no relation with their attitude toward the online educational experience. The finding of the study can be beneficial for online activity course designs in the future. Apparently, student participation is considered a vital variable; thus, motivation strategies are to be carefully planned to facilitate effective online learning.