Hi Harthwirt
Have you got the 'Find my iPad' setting on. At least you can narrow down its location.
Hope you find it soon. FWIW my iPhone fell out of my bag on a long distance bus. Find my phone had been turned off. I got my OH to eventually text my phone and the person saw the notification and immediately phoned back. It was with bus company. If you've got notifications turned on - maybe send an alert with contact details?