An exemplary posted information sharing system includes: a game processing unit configured to execute a multiplayer game application through a plurality of users each using a terminal; a group formation unit configured to form a playgroup for playing the game application, wherein the game processing unit includes: a group formation request unit configured to output, to the group formation unit, a playgroup formation request that specifies a group, according to input of the terminals, wherein the group formation unit is configured to form the users of terminals that specify the same group into a playgroup, based on the specified group.