Is PRP useful for naturally thin hair with no underlying medical condition?

Hello,
Yes prp is a great treatment. It takes more than 1 session to see the benefits. Minimum 3-4 times in a year

Hair loss has many causes, including stress, medications, autoimmune, genetic, trauma, etc. Medical treatments can work and options would include finasteride (propecia), minoxidil (rogaine), PRP (platelet rich plasma), laser light therapy, and vitamins. It is often uncertain which medical therapy will help which patient and so a combination of therapies is typically recommended to maximize benefit. A hair transplant is a surgical option and is appropriate for certain conditions and individuals. PRP can definitely be effective in the right candidate. Consult with an experienced hair restoration surgeon for a complete range of options that are appropriate for your situation. 
Gary Linkov, MD
Hair Specialist
Manhattan

prp and a cell can help improve thickness of the hair and growth factors with roller once weekly can help.  oral vitamins also help (see link).
I suggest a formal consultation as there are a combination of treatments that can be done to improve har loss.  Oral finesteride has very little to no side effects in the majority of people; PRP/platelet-rich plasma + stem cells like A Cell help regrow hair and slow down the thinning process; rogaine and restorsea spray should be used daily; oral viviscal helps keep nutrients high in the follices as well.  Transplantation is a last resort but works early in the aging process as well.  A formal consultation and combination treatment is needed.  Best, Dr. Emer. 

The length and density of hair are determined by your genetics. If you have always had thin hair since childhood then PRP is not going to make your hair thicker. If it is someone who has had a change in hair from thicker to thinner than PRP will be beneficial to help to rethicken hair. You should consider using a supplement like Viviscal or Nutrafol first before PRP to help encourage hair growth.

Excellent question. It sounds that you don't have hair los so, I don't think that PRP will have some benefit for a genetic thin hair and your hair won't be thicker. But you can use any hair thickening products. Good luck. 

If you have generalized uniform thinning hair, there is nothing you can do medically; however, there are thickening agents you can purchase which can substantially thicken the hair.  Get these from your stylist