The study aimed to scrutinize social networking effects on Iranian EFL learners’ vocabulary acquisition. Eighty Iranian EFL learners at the intermediate level participated in a pretest-posttest study after taking the placement test. They were then divided into an experimental group whose participants were supposed to equip their mobile phones or tablet PCs with a social networking application, that is, Line and form an online group to take part in eighteen virtual instructional sessions. Participants of the control group, however, underwent classroom learning during which target words were presented through routine classroom activities. Results of the independent-samples t-test in the posttest indicated that participants of the experimental group outperformed those of the control group. Results have important implications for both pedagogy and theory, especially socio-cultural theories of second language development. Manuscript profile