The present research delves into the concept of celebrity co-creation from the consumer behavior perspective. It explores the impact of the degree of a celebrity's involvement with a brand (celebrity as an endorser vs. celebrity as a co-creator) on consumers' advertisement and brand-based evaluations (Study 1) and purchase behavior (Study 2). The research subsequently incorporates the mediating effects of consumers' perceived risk (Study 3) and the moderating effect of celebrity expertise (Study 4) in the relationships. Three of the four studies were controlled experiments among nonstudent samples (combined n = 486), while one was a field study. Major findings indicate that a celebrity co-creator is more effective than a celebrity endorser, but both cases of celebrity presence are more effective than the control (Studies 1 and 2). This effect is observed to be mediated by the consumers' perceived risk (Study 3) and moderated by the celebrity's expertise (Study 4). The present research provides a new direction to value co-creation research from the communications perspective and adds to the literature on celebrity endorsements.