First of all it is essential to determine the type of hair loss you have. Hair transplant is an accepted mode of treatment for androgenetic alopecia but not for others. Further, it should ideally be done only after full development has taken place (and that there is no further progression) and when all other methods of treatment have been ineffective. In general, younger the patient, more conservative should be the treatment. As far as I know, stem cell therapy for hair loss is still in experimental stages.