1. A system using a server comprising a processor for providing a social network service, the system comprising: a community searching unit configured to extract a profile of a first user based on a frequency of keywords in a first document received from the first user and to determine communities by searching for one or more communities based on whether the one or more communities currently having similar interests to that of the first user, the determination is being performed according to the profile based on a time interval; a document registration unit, executable by the processor, configured to transfer the first document to the one or more determined communities, and to receive a second document related to the first document, the first document being displayed to users of the one or more searched communities via a first interface, and the second document being displayed to the first user via a second interface, the first document and the second document being displayed in a manner distinguished from a third document using the first interface and the second interface, the third document having been registered in the one or more searched communities; and a document providing unit configured to provide the second document to the first user not registered as part of the one or more searched communities.
4. The system of claim 1 , wherein the community searching unit is configured to provide, to the first user, a candidate community group comprising at least one community associated with the first document, and the document registration unit is configured to receive the second document registered by a second user in a community selected by the first user from the at least one community of the candidate community group.