1. A method comprising: obtaining access, by at least one computer processor, to a relationship network; obtaining access, by said at least one computer processor, to a similarity network; obtaining, by said at least one computer processor, a user query directed to a node in said relationship network; and carrying out a multiple heterogeneous networks search combining at least said relationship network and said similarity network, by said at least one computer processor, to obtain a ranked output list responsive to said user query directed to said node in said relationship network; wherein said ranked output list comprises at least one node other than said node to which said user query was directed, wherein said carrying out of said multiple heterogeneous network search comprises: examining, in said relationship network, direct neighbors of said node to which said user query was directed to find a solution to said user query; responsive to said solution to said user query not being found via said examination of said direct neighbors of said node to which said user query was directed, examining, in said similarity network, for a node similar to said node to which said user query was directed, to obtain a list of candidate nodes; and searching said social network in an extended neighborhood of said node to which said user query was directed to rank said list of candidate nodes based on closeness.