Embodiments of a distributed instant messaging system that uses a distributed index in peer-to-peer networks. A distributed index may be used to implement an instant messaging system in a group of participating peers. The distributed index may be used, for example, to route messages between participating peers, in identifying and authenticating peers wishing to participate, in notifying peers of newly joined peers, and in notifying joining peers of participating peers. In one embodiment, zones of the distributed index may be moved to joining peers. In one embodiment, zones of the distributed index stored on departing peers may be moved to participating peers. One embodiment may be implemented in peer-to-peer networks implemented according to a peer-to-peer platform including one or more peer-to-peer platform protocols for enabling peer nodes to discover each other, communicate with each other, and cooperate with each other to form peer groups and share network resources.