I lost it in the morning or very early in the afternoon, because the wind was south and very light at one point.
It has a so called watchdog on it, this is a qr-code which you can scan with any smartphone or tablet and gives contact details, only thing is right after I lost it I hadn't activated that yet since i didn't know. But it is now, so maybe someone already looked and never looked at it again. You get this URL when you scan the code: http://switchkites.com/snl.php?sn=1312T018 and that php script eventually redirects to this direct URL http://switchkites.com/watchdog/kite/scan/sn/1312T018
Edit: Sorry I forgot for a pretty long time to write back on this forum to say that someone found my board eventually, it was someone from https://www.itfryskegea.nl/