See all devices using my Apple ID

Hello all.

I woke up this morning to a message that my Apple ID is now being used for iMessage and FaceTime on a new Mac.

It also says if I recently signed into "David Mac Pro", I can ignore this notification.
Great... but what if I didn't? No help there?

I think this is related to the fact I sold my old mac pro around 3 months ago. I'd wiped everything off of it but not done solid reinstall, due to Apple making it nice and difficult to do so unless you want the latest OS X (Yosemite is useless for music production.)

I googled around, and the only help I can find is to view devices which use your Apple ID for ITUNES. There's nothing else, only help for iTunes accounts.

I checked there anyway; only devices recognised on iTunes are my iPhone and old PC. Even my current MacBook isn't listed there which uses Apple ID for quite a few things.

So, how can I see what devices are using my Apple ID?

At the end of the day this isn't a -huge- issue, as I never use FaceTime or iMessage - none of the people I talk to use them so I can't either, and as I know who it is that is signed in (and they're probably totally unaware), I know it's not a massive threat. But, I'd like to get it sorted anyway.

(Also, there's no community for Apple ID (helpful yet again Apple.), so had to post in FaceTime as the closest section.)