The invention discloses a communication system for assisting a user for retrieving geography-associated multimedia information, and the communication system comprises a data processing device and several mobile communication devices. The data processing device receives a first request information including a location term and a time term from a terminal device of the user, and broadcasting a second request information, based on the time term, to the mobile communication devices located within a region relative to the location term. The data processing device receives responding messages and captured audio and/or video data from the mobile communication devices accepting the second request information, and transmitting a location-related information to the terminal device based on the responding messages. The user transmits responding information responsive to the location-related information to the data processing device via the terminal device. The data processing device transmits the captured audio and/or video data (representative of the retrieved geography-associated multimedia information) relative to the responding information to the terminal device.