This is a very common problem faced by boys, who have not studied in coeducation (boys and girls together in school). Your problem is to take initiative in talking with girls. Best way to curb the fear is to face it. So try to talk to the girls whenever you get the chance. You may talk long on phone after your initial introduction. This may give you more confidence. Most of the girls will understand your shyness and will support you to overcome if you sound intresting to them.Try to maintain one or two relations and that’s it. I understand that it may not be that simple but you need to put conscious efforts and overcome your shyness. If you do not get success, you may try self-hypnosis to overcome your fear. There are medicines to overcome your shyness; you need to consult Psychiatrist for this.