In this paper, we propose a tracker-based Peer to Peer (P2P) system for live multimedia streaming services. Our system is based on the Proactive network Provider Participation for P2P (P4P) framework which induces the cooperation between P2P systems and network service providers to achieve the best possible P2P application performance and efficient and fair usage of network resources. In the proposed scheme, the P2P application server obtains the network status information from servers of network providers. Also, the P2P application server receives the upload/download link capacity and the stream availability information from each peer. With the above information, the P2P application server suggests a peering list for the newly joining peer. The peering considers the routing cost, the congestion level of the links, the end-to-end delay, the matching of the upload/download link capacity, and the provision of the stable streaming service. We also propose a playback synchronization mechanism that enables each peer to start the playback within the limited variation from the playback positions of source peer. Through the simulation results, it is shown that the proposed peering mechanism enhances the playback continuity and system stability, and reduces the control overhead. Also, the playback synchronization mechanism shows the better performance with respect to the variation in playback positions of peers in the entire system.