A system comprising a personal information management server connected to at least one personal information database configured to store first personal information regarding a first user and second personal information regarding a second user, the first personal information including personal information of one or more acquaintances of the first user, the second personal information including personal information of one or more acquaintances of the second user, the personal information server being connected to a network; and wherein the system is configured to determine a degree of similarity representing a number of mutual acquaintances shared by the first user and the second user, control to indicate, at least using a first communication device of the first user, the degree of similarity representing the number of mutual acquaintances shared by the first user and the second user, transmit over the network, from the first communication device of the first user to a second communication device of the second user, a request to perform a subsequent communication between the first user and the second user, and in response to an instruction, from the second communication device of the second user, to accept the request to perform the subsequent communication, establish the subsequent communication.