What is the success rate of PRP treatment for hair loss?

In my opinion, it depends how you evaluate success and what diagnosis you are treating and if the protocol is adequate.  For androgenic Alopecia, if one is assessing shedding, the chances of it decreasing is approximately 40 to 80 %. Increasing the diameter of the hair shafts has about the same percentage. Hair regrowth is difficult to predict. If the hair loss is less than 3 years the chances of regrowth are good. If the follicles are lost, there will be no PRP induced regrowth. Find a PRP expert. As to see photos.

Most people do grow hair after PRP treatments.  How much hair will vary.  If the cause is androgenic alopecia (too much male hormone), the likelihood is good.  If there is a different underlying cause then addressing and treating it (adding medication, iron, etc.) plus PRP  will be helpful to get optimum regrowth.