The internet provides information media and social media for online consumers to seek information on the websites and opinions from other consumers. This study examined how the three dimensions of interactivity (control, communication direction, and synchronicity) affected users’ online information seeking process. Particularly, this study assessed how cognitive involvement and perceived social presence mediated the effects of interactivity onto satisfaction of websites, purchase intention and spreading word-of-mouth. Moreover, we also investigated how users’ opinion leadership moderated the effects of interactivity. This study recruited 511 respondents to participate in the survey. The results showed that control and synchronicity positively influenced consumers’ involvement, which further mediated the effects of these two dimensions of interactivity onto user satisfaction of the website, purchase intention and spreading word-of-mouth. On the other hand, communication direction and synchronicity positively affected their social presence, which only mediated the effect of synchronicity onto those three dependent variables. Lastly, users’ opinion leadership moderated the effects of communication direction and synchronicity on social presence, but did not moderate the effects of control and synchronicity on involvement.