As a promising standard of television, IPTV gains increasing popularity with its on-demand services. However, supporting scalable on-demand IPTV services remains to be an important challenge. Existing IPTV architecture dedicates a regional station to serve subscribers in the respective region regardless of temporal and spatial dynamics in service demand. This may cause significant imbalance of resource utilization and service provisioning delay among stations, especially with increasing subscribers and service catalog. In this paper, we propose CiTV, a Collaborative Internet TV service platform that achieves efficient and scalable IPTV service delivery through inter-station collaboration. First, CiTV employs a novel request dispatching algorithm that enables stations to autonomously dispatch requests among themselves and achieves low per-view cost and load variance at the same time. Second, CiTV also leverages a distributed content placement algorithm to globally optimize content utilization at multi-station level, which is important for deployment scalability. Last but not the least, CiTV also ensures service delivery quality and efficiency through fine-grained collaboration scope control.We perform both theoretical and empirical analysis of CiTV. Our experiment results suggest that CiTV significantly improves the scalability of on-demand IPTV services for the existing IPTV architecture.