I can't find the debug.keystore file
Open Eclipse Preferences, then navigate to Android > Build. There you'll see a field that tells the location of your debug keystore.
On Linux / OSX use your favorite terminal and type rm ~/.android/debug.keystore to remove the debug keystore.
You can create a new keystore after that by following these steps.
I believe it is in the .android/avd/ directory in OSX, but it could also be just in /.android/ as you suggest.
Remember that ~ means your home directory, so you do not need to look for it in your SDK!
(disclaimer) It's been a while since I've battled with this, and I didn't do it on a mac.