Try to remember as much as possible about this man. Its precise name, surname and patronymic, year and place of birth. It may help his number. Page through all the old phone books, you might find his number, even invalid. Call friends, who he might be. You remember, perhaps, in conversation, he mentioned, which transport goes, some companies and shops in his neighborhood, in a school or a clinic he served. All this will help to narrow the geography of your search.
Find as many phone books in Saint-Petersburg. Especially suitable for the old print edition, specifying the address by name. It often happens that the urban room is cleared, but people continue to live in this house. Some electronic telephone directories also provide not only the phone number and address.
If you are in SaintPetersburg, refer to the Central address Bureau at the address: Foundry Avenue, building 6. Come there in person and fill out the form according to the information that you have. If you are interested the information is there, provided for a fee.
Use the electronic databases, such as www.nomer.org/spb, spb.telkniga.com, interweb.spb.ru/phone. The more precise information you provide, the less will be the list of addresses. Enter the information you have and click search. The system will provide you with a list. Knowing his name, first name, email address and the exact date of birth, there is a good chance to find it in social networks.
Make a list of the most suitable locations. Call or personally visit all of them. If an independent search was fruitless, try, use the services of private detectives.