A method by which a service system including an instant messenger server provides users with a service for raising a cyber pet and making friends through the cyber pet, includes the service system's providing and installing an instant messenger program to a user; receiving, storing and managing the user's friend list; displaying a cyber pet on the user's client terminal when an instant messenger active window is opened; and in the case that the user does not raise the cyber pet for a predetermined time, receiving the user's friend list and friend lists of another users hierarchically linked thereto, forming a potential friend list from the collected friend lists of another users, moving the cyber pet to the friend list and the potential friend list of the user, and displaying the cyber pet to another user executing the instant messenger.