<![CDATA[The increasing concentration of regulatory power within digital platforms has transformed online intermediaries into influential actors that shape public discourse, regulate information flows, and determine the conditions of digital participation. Existing scholarship on digital constitutionalism has extensively examined platform governance, algorithmic regulation, and content moderation; however, limited attention has been devoted to the democratic foundations of platform legitimacy and the role of digital citizens in constituting legitimate governance structures. This article addresses this gap by developing a socio-legal theory of Participatory Platform Constitutionalism (PPC), which reconceptualizes digital citizenship as a normative source of democratic legitimacy in platform governance. Employing qualitative socio-legal and conceptual legal research, the study analyzes contemporary debates on digital constitutionalism, algorithmic governance, democratic legitimacy, and digital citizenship through an interdisciplinary theoretical framework. The analysis demonstrates that existing platform constitutionalism models remain constrained by procedural approaches emphasizing transparency and accountability while neglecting meaningful citizen participation. The article argues that democratic legitimacy in algorithmic governance requires the institutionalization of five interconnected constitutional rights: participation rights, contestation rights, algorithmic transparency rights, data sovereignty rights, and collective oversight rights. By integrating digital citizenship theory into digital constitutionalism scholarship, this article proposes a new framework for evaluating and reforming platform governance, contributing to ongoing debates concerning democratic accountability, constitutional ordering, and regulatory legitimacy in the digital age.]]>
