A plurality of communication devices are configured for communicating with the server via the internet. Each communication device is configured for communicating with other communication devices, via short range signals. At least a property of the received short range signals is measured and converted to signal data. Each communication device is associated with a user, and each user is associated with respective user data stored. Location data of at least a first communication device is known at a first time. When a second communication device is inside the communication ranges of two or more first communication devices with known respective locations, the server processes the known locations to yield a location of the second communication device.