1. A method of identifying a sub-graph in a network, the sub-graph similar to a sample sub-graph, the method comprising: identifying at least one sample key node of the sample sub-graph; selecting at least one key node similar to the at least one sample key node, wherein the network includes the at least one key node; forming at least one group; expanding the at least one formed group into a corresponding sub-graph candidate; and comparing the sub-graph candidate with the sample sub-graph to identify a similar sub-graph.