The increasing need to compete in innovation and the prevalence of IT in social and economic interactions have led to greater globalization in innovation sourcing, particularly through online crowdsourcing platforms. Crowdsourcing platform participation, a phenomenon inadequately covered, is an instance of providing an innovative solution or idea intertwined with personal and social factors that interact to result in a behavior. A better understanding of the impact of social factors and participants' hedonic, utilitarian, and social motivations can guide the design and management of these crowdsourcing platforms to foster sustained engagement. This study considered the competitive and social nature of these platforms and analyzed participation intentions from a novel standpoint-a combination of motivational and socio-cognitive perspectives and their relationships within two different types of crowdsourcing platforms: Atizo's third-party-hosted community and Nokia's brand-hosted IdeasProject community. A comparison of these two types of crowdsourcing platforms for the same activity of ideation at an individual level revealed differences in behavior determinants based on the platform host type, domain specificity, and mechanisms supporting different motives and social factors.