Has your hair always been thin or is it a recent thing? Is it thin (as in the number of hairs) or is it very fine in texture?
There is no way to add hair follicles that were never there. If they were and have stopped producing hair, there are things you can do.
Hair Loss links If your hair is just very fine or has always been thin, perhaps you need a different hair cut. This would mean going to an experienced hairdresser or barber stylist and asking for their advise as to the best cut.
If you would like to post a picture. We can give you some ideas. <img src="/images/graemlins/smile.gif" alt="" />