Hi there, it is perfectly normal for babies to not have hair at that age. In fact, my cousin's baby was pretty much bald till she turned one. Then all of a sudden, hair grew and now at 3 years, she has the thickest, shiniest head of hair. Don't worry too much about it. As for helping the hair grow, I've heard of friends who used olive oil or coconut oil but they usually use it when baby is older.
does your baby's scalp look healthy with no skin irritation? if so, it's perfectly common for babies to not have any hair! here's some more info: http://www.newkidscenter.com/When-Do-Babies-Start-Growing-Hair.html
Heard can use olive oil