Look in Interact->Email when editing your game. Not sure exactly who it does and doesn't go to, but might be worth a try.
Thanks for the speedy reply.
I poked around a bit and discovered that the CSV export file contains all of the information, including the donor's email address.
Just a side note, are you sure you want to contact someone who decided to donate to you anonymously?
You know, that is an excellent point. I was just so excited that someone liked my game enough to cough up some dough.
Luckily, you stopped me in time. Thanks.