In the past few years, there has been an increase in the use of social media for language pedagogy. While some high-profile social media platforms have been extensively studied, their potential as an electronic portfolio (e-portfolio) is under-researched, particularly in the area of L2 (i.e., English) speaking. Thus, this study fills in the vacuum by investigating the effects of social media as an e-portfolio platform for the speaking performance of L2 students whose L1 is Chinese. Using a quasi-experimental design, the findings demonstrate the viability of a social media-based e-portfolio for significantly improving college students' speaking performances. These results were linked to three factors, namely the (a) social pressure from high visibility, (b) sense of captive audience, and (c) increased level of engagement due to the interactive features of the platform. Some technical and learner/learning-related challenges were also reported by students. Implications for L2 speaking pedagogy, assessment, and future studies are discussed.