We examine how multi-platform digital environments influence intra-party dynamics within political organizations, focusing on the Italian Five Star Movement (M5S) as a paradigmatic case of extreme digital party. Leveraging a unique dataset spanning five online platforms central to the M5S community – Beppe Grillo’s Blog, the M5S Forum, Meetup, Facebook, and the website of the M5S 2012 online primaries – this research classifies platforms based on their affordances (visibility and associability) to analyze cross-platform activity, communication patterns, and candidate selection. The findings reveal the fragmented nature of multi-platform environments in fostering simultaneously centripetal and centrifugal dynamics within political organizations, highlighting critical implications of digital platforms for intra-party dynamics. We identify significant differences in platform affordances, with communication emerging as either top-down or horizontal. Cross-platform engagement is limited and asymmetric, with grassroots-oriented platforms fostering cross-engagement as opposed to top-down platforms, reinforcing boundaries that hinder internal cohesion. Leadership communicative influence varies across platforms, suggesting that user behavior and platform design mediate leadership power. Candidate selection reflects both leadership and grassroots dynamics: candidates’ success correlates with local network centrality on Meetup and alignment with leadership messaging on Facebook. Our study reveals how multi-platform environments generate fragmented patterns of internal communication and influence within political parties when they progressively increase their exposure to the mediation of digital technologies and provides insights into their broader implications for democracy, given the centrality of parties in elite selection and the functioning of democratic systems.