Question: Recently, I find out that somebody uses my network traffic. I found his `MAC` address and now I wanna find full details of his device. I tried: <http://www.macvendors.com/> and such this, but the response was only the name of manufacture. Tnx from anybody who helps me( or says a better solution to find him:) )
EDIT: Anybody who has another way to find him, tells me.

Answer: 
I have another idea for this purpose: what if somebody , on purpose , set own wifi without any password and the thief could connect again!

I think in that case we have more chance to discover what device is connected to our router.
It is not possible to get device details via MAC address as @Hennes already said as the MAC address is only specific to the network card.

Another way to obtain more information is to log into your router/firewall and look for known devices with the found MAC. There you have the association MAC <-> IP address. 

You the can use tools like nmap/zenmap to gather more information.

If you are just after locking him/her out of your network it may be possible (depending on your router) to block access for the device with the specific MAC address.