This paper explores the growing regulatory role of very large online platforms (VLOPs) through the lens of digital constitutionalism. It argues that while these platforms operate under private legal frameworks, their governance functions—especially content moderation and algorithmic decision-making—closely resemble public regulatory authority. As platforms increasingly shape the terms of civic participation, public discourse, and access to information, a normative gap has emerged between the private character of their power and its public consequences. The study identifies three core questions: what motivates platform self-regulation, whether platforms exercise public-like functions, and whether digital constitutionalism provides a viable framework for constraining their power. Drawing primarily on a comprehensive literature review, the analysis confirms that platform self-regulation is strategically motivated, that platforms exercise quasi-public authority, and that digital constitutionalism offers a promising—though still evolving—response. The findings suggest that constitutional values such as transparency, due process, and the protection of fundamental rights must increasingly be applied to powerful private actors in the digital environment to uphold rule-of-law standards and democratic legitimacy.