Many unstructured overlay-based peer-to-peer (P2P) applications require techniques that can effectively send messages to various topological regions of the overlay. While searching in unstructured P2P networks has been widely studied in literature, the problem of diffusing messages to various parts of an arbitrary overlay network has received surprisingly little research attention. In this paper we analyze the message diffusion problem and make two technical contributions towards addressing it. First, we propose a novel message propagation technique called the Cluster Resilient Random Walk (CRW). While the CRW technique preserves the overall framework of random walks, at each step of message forwarding, it favors the neighbors that are more likely to send the message deeper into the network. Second, in order to ensure effective message diffusion in networks with small cuts, we introduce a unique message fission technique in which messages are split when they reach peers connecting two or more topological regions of the network. Our experiments show that the proposed technique are very effective in diffusing messages across overlay networks of various topologies.