In China, the implementation of a Danmaku social media system to sustain and raise user interest in online video sites is an increasingly widespread phenomenon. Danmaku technology is used to display users’ messages in written text on the online video stream. Little is known about the effects of this form of interactive enhancement. The aim of this empirical study is to evaluate the evolving media capabilities of the Danmaku system and their effects on users’ perceptions of interactivity and their intentions to continue using Danmaku. We draw on media synchronicity theory and apply it to a stimulus-organism-response model. Using this framework, we hypothesize that the media capabilities of the Danmaku system, namely its transmission velocity, parallelism, symbol sets, rehearsability, and reprocessability, elicit increased interactivity, which influences users’ instantaneous intentions to share and to continue the use of the Danmaku system. The results showed that both users’ instantaneous intention to share and their intention to continue to use were significantly affected by the perceived interactivity. Unlike the results of previous studies, our findings showed that all five media capabilities positively affected the users’ perceptions of interactivity. The potential theoretical and practical implications of our findings are discussed.