I am 27 and have been using Propecia for 3 years but my crown is still thin. What can I do?

If the finasteride has not solved the problem by this time in your crown and you have some hair present you have three options.
1- Do nothing and live with it
2- Get a hair transplant which may solve the problem as that is what I did. My bald crown is now full looking
3- Get Scalp Micropigmentation which will make your thin crown look full as shown in this website photo below (click image to enlarge)