I am an Intl student on F-1 who worked on campus in 2009. I thought since my income was under tax treaty exemption- I didn't have to file taxes. I was wrong.

What forms do I fill now that I am filing late?

You will just have to file a late payment form with your form and pay a penalty. Given how much time has passed, your international status, student status and the fact that there have been some significant tax changes since this return was due, you should go see a tax preparer. I feel comfortable recommending H&R Block for this. They will be able to make sure this is done properly for you and you can generally get in the same day you call.

I would not attempt to resolve this yourself because there are too many variables and you risk over paying or missing some credit or benefit that's owed you. If something is filed late, and then you also make a mistake, it can flag your return for audit which is a huge hassle - so yeah, go to a tax preparer and let them help you do this properly.

Since I owe no taxes, I don't why know why there would be a penalty?

As far as I know H&R Block etc have no clue about F1 stuff. They file mainly for residents and will more likely than not screw this up.

I was hoping AtlantaTaxExpert can chime in

If you owe no tax, there will be no penalty. Sorry for the late answer; been busy.

Email me at the email address in my profile with your W-2 and details and I will evaluate and comment in detail.