Refer to social networks, for example Vkontakte, Odnoklassniki, Facebook and others. Find page other information available to you (surname, name, patronymic, year of birth, school or Institute), and write him a message, asking him the phone number. If the page other can't find yourself, try to implement with the help of common friends who will gladly share his phone number.
Get a directory of phone numbers of your city or region. Some of them allow in addition to finding people in the room to perform the reverse operation. Often you can find these guides in electronic form. They can be purchased, for example, in the departments of electronics. Be sure to check the legality of the actions performed, and beware of scams that often sell illegal databases of cell numbers. Download the guide from the disk, enter the coordinates into the appropriate fields and get a room that interests you. The information obtained may not always be accurate, so check it carefully.
Try to find a friend's number or friend with the help of law enforcement. The police person can quickly "punch" through the database operators through a formal request. Perhaps they will be able to help you to find him.
Contact private detective. Recently there has been dynamism in the development of the market of detective services. Private agencies usually former employees of intelligence and law enforcement agencies that can find your friends in a matter of hours. But we must remember that this service is quite expensive. This method should be used after you have tried the rest and they did not bring the desired result.