A method of tracking a lost mobile electronic device connected to a wireless or wired network is provided. The method includes: storing user identity information included in a user identity card inserted into the mobile device, a warning message, and information regarding a destination of the warning message; and when a new user identity card is inserted into the mobile device, comparing user identity information stored in the new user identity card with the stored user identity information and automatically transmitting the warning message to the destination of the warning message if the user identity information stored in the new user identity card is not identical to the stored user identity information. Accordingly, it is possible to easily track a lost mobile electronic device connected to a wireless or wired network.