Max just go in person,they are VERY helpful. It will be easy to get HKID for you. My GF wasn't even born in HK, but since her parents were she was able to get it. You'll be under a different section, but you'll be able to get it, no problem.
Go in person and they will tell you exactly what to do.
I think at first you will need photocopies of documents such as your birth cert. your USA immigration card, and your parents' HKID's, etc. That will get the process going. Eventually you'll need to go to the immigration centre in Wan Chai IN PERSON and show them the original documents. Then you'll get your picture taken right there (on another floor) and they'll send your card in a few weeks.
You can't get it without being here. Your parents don't have to be around, but you'll definitely need one of them to lend you their original documents (use FedEx)