1. A method of recommending content to a first user by using one or more second users in a peer-to-peer (P2P) network implemented by a processor, the method comprising: receiving, via the P2P network from the one or more second users meta data regarding content belonging to the one or more second users; detecting a plurality of pieces of recommended content similar to content that the first user is currently using, based on both the received meta data and the content that the first user is currently using, by searching the received metadata from the one or more second users for the plurality of pieces of recommended content which are similar to the content that the first user is currently using; and outputting information regarding respective pieces of the detected recommended content, wherein the one or more second users have a content preference similar to a content preference of the first user, wherein the information regarding the recommended content is included in the metadata received from the one or more second users, wherein the one or more second users belong to at least one of a plurality of second user groups which are classified according to a classification criterion, wherein the detecting the pieces of recommended content comprises detecting the pieces of recommended content according to the classified second user groups, and wherein a first group among the plurality of second user groups includes users that have preference similar to the first user preference relating to a first classification criterion selected by the first user for recommending a first type of content, and a second group among the plurality of second user groups includes users that have preference similar to the first user preference relating to a second classification criterion selected by the first user for recommending a second type of content.