I'm 18 year old guy, I don't have facial hair. Please suggest a solution

Facial hair growth is determined by inheritance.  There is no way to grow facial hair faster or grow hair that is never going to grow.  It is not a disease.  It is just they way you were born.

The amount of facial hair you will develop is genetically determined. So is the age at which your beard and moustache will start to grow. Be patient. Either it will grow or it won't. When you are older, a hair transplant procedure is an option but you are much too young to consider this now.

You need to wait as you are still young and may still grow out more facial hair.  If after a few years you still have thinned out mustache or beard you may consider hair transplant at that time. 

Simply put, many men of your age are slow to develop beard growth. Ask you dad when he started to grow his beard out. Maybe you will follow his pattern. In any event, just wait for another 5+ years and see what happens.

If you have a full head of thick coarse hair, hair transplantation with hair taken from your scalp and placed in the bearded area of the face might be an answer for you.