Organizations increasingly rely on new forms of organizing for innovation that are semiformal. A typical example is represented by the implementation of web-enabled ideation platforms through which employees can provide innovative ideas, interact and contribute to the innovation process beyond their present work responsibilities. However, limited attention has been placed on investigating the organizing structures of these virtual initiatives for innovation. Based on data collected from an online ideation platform of a large European organization, we combined cluster analysis, social network analysis and interpretative content analysis to explore how employees participate to these initiatives and how they differ in the content and outcomes of their contributions. We supplemented these data with semi-structured interviews to generate more insights into employees’ underlying motivations to participate to these initiatives. We identify a typology of five employee roles characterized by different behavioral contribution patterns and which differ in their communicative practices. Our findings particularly suggest a key difference in the contributions made by active and marginal members. While more active employees play a key role as innovators, having their ideas more likely to be selected, the key contribution of more marginal members lies in the elaboration phase of the idea journey by providing different types of feedback directed at supporting and complementing submitted ideas. Our findings also suggest similarities and differences in the motivations for participation underlying the identified employee roles. Implications for innovation research and practice are discussed