Driven by the consumer demand for companies to be socially responsible, companies are increasingly relating their brands to causes and charities in order to accomplish nonprofit objectives and corporate sustainability. In a social marketing campaign, the consumers’ choice of the cause can influence their reactions through the processes of choice. Allowing the consumers to choose the cause may also reinforce their personal role in the donation process, which may result in a better outcome. Further, advertisers are paying increasing attention to the launch of social marketing campaigns via social media, since social media has recently become an essential part of daily life and therefore an imperative venue through which companies connect with consumers. Focusing on the rapidly evolving social media landscape, this study primarily clarifies (1) how choice influences consumers’ perceived interactivity with a social marketing campaign in the social media context, and (2) consumer involvement, as consumers’ individual differences can enhance or limit the effects of a social marketing campaign with choice. Using field experiments, this study investigates the relationships between the consumers’ choice, perceived interactivity, attitude, and purchase intention, and considers the moderating effects of involvement on those relationships. This study’s contributions are that it illuminates (1) the effects of choice on the perceived interactivity of social marketing campaigns in social media contexts, (2) the role of involvement in social marketing campaigns as a moderator, and (3) attitude and purchase intention as outcomes that can facilitate the construction of a theoretical model for social marketing campaigns with choice in the social media context and offer possible implications for advertising practitioners.