In this paper, we propose DINPeer, an optimized peer-to-peer (P2P) overlay network for service discovery by overcoming limitations in current multicast discovery approaches and P2P overlay systems. DINPeer exploits a spiral-ring method to discover an inner ring with most powerful nodes (DIN Nodes) to form a logical DINloop. With the facilitation of the DINloop, multiple DIN Nodes easily form Steiner trees using Steiner tree-based heuristic routing algorithm. DINPeer further integrates the DINloop and Steiner trees with the P2P overlay network. The key features of DINPeer include that multiple DIN Nodes function as the Rendezvous Points (RPs) for theirs associated logical spaces respectively, and Steiner trees facilitate the communication among multiple DIN Nodes. Multiple powerful DIN Nodes release the burden on the centralized server and the self-recovered DINloop avoids the single point of failure. Simulations show that DINPeer is able to reduce multicast delay for the fast service discovery.