If you don't know neither the name nor the name of the person, try to start looking from the place where you met him. For example, if it happened at a certain stop or subway station near the office building, University, etc., try to arrive there at the same time (or day of the week). It is likely that the person will appear there again, and you will have the opportunity to talk with him.
To find a person without knowing the name, the description of his appearance. Try to contact the people you will see near where you you'll rendezvous with the one you are looking for. Ask if they've seen here, for example, a girl with long dark hair, brown jacket, messenger bag, etc. you May tell me what time and where you will be able to see a welcome face.
Try to search for a person via the Internet. Especially can help in this social network where there is community interest on this issue. In the group from your city, leave a message with the request to help to find the right person and description of his appearance. For example, say that you liked a strange girl, and now you want to meet her. Pretty high chances that subscribers not only to report the name and surname of the person, but will share with you the link to his page in social networks.
Much easier to find a person with his photo. For example, you want to know the name of the one who imprinted on a photo you saw in the newspaper or online. Try to print and show this photo to people in the places where he can work, study or relax. You can also post the photo to appropriate groups in social networks, on sites free of ads and other thematic information resources.
There is an assumption that people are connected to each other through their friends and acquaintances. So if you want to find a person, even not knowing the name, just ask for help in all your friends and relatives. They, in turn, may be asked to do is of people from your social circle. In the result, sooner or later you will learn about this person from someone or from any other sources of information.