— We present the Adaptive Group Notification (AGNO) scheme for efficiently contacting large peer populations in unstructured Peer-to-Peer networks. AGNO defines a novel implicit approach towards group membership by monitoring demand for content as this is expressed through lookup operations. Utilizing search indices, together with a small number of soft-state shortcuts, AGNO achieves effective and bandwidth-efficient content dissemination, without the cost and restrictions of a membership protocol or a DHT. We present several simulation results over different topologies using both synthetic and real workloads, to evaluate its performance. Our method achieves high-success content transmission at a cost at least two times smaller than proposed techniques for unstructured networks.