Although the evolutionary pathways are critical to the success of platforms, extant literature has provided little insight into the dynamic processes of the platform evolution, let alone how platforms constitute the evolutionary pathways over time. Against this backdrop, this study examines the evolutionary path constitution of platforms by adopting an organizational momentum lens. Through an exploratory case study of Pinduoduo, it provides evidence of path dependence under the network effects and of path creation resulting from the deliberate actions conducted by the platform firms. Moreover, this study identifies three platform strategies to manage its momentum to facilitate platform evolution and sustainability. Furthermore, this study develops a holistic framework to explain the interactions between platform momentum and path constitution by considering the outcomes of these strategies. The findings and developed framework shed novel light on the path constitution of platform evolution and provide new insight into the sustainability of the platform firms and platform-based markets by leveraging momentum thinking.