The first thing anyone will suggest you do is to check with your health care provider.
They can test you to see if your hair folicles are healthy, and if your hormone levels are normal. Is the rest of your body hair growing normally?
Another thought just cropped my mind.. Do you have any American Indian (or Native American) ancestry? If so, you might not develop full facial hair.
So, please see your doctor for reassurance..
P.S.
I'm assuming that you are not taking any steroids that you should not be taking, as that can prevent healthy hair-growth too.