If you are searching for any domain owner in the web, then you will enjoy the ease of use of this nice WhoIs tool. You just have to enter the domain name with the top-level-domain and that's it (e.g. "easymarketplace.de").
So, you normally leave out the "www" in front of it. But, mostly this works as well, if you type it in as well.
The most likely best tool for this in the internet is:
Another tool is the Universal Who Is Search:
(Do not be surprised, if this tool does not work after several requests any more ...
There is a limit of requests per IP adress per minute built in. So, either you go to the internet with a different IP adress or you just wait a few minutes in order to request the next domain. This is designed this way in order to prevent "automates" from grabbing information of this who-is directory.)
If you want to have a deeper look into the whois tool you should go to www.uwhois.com
The only top level domain, that does not work this way, is .gov as the who is server for this domain is permitted for US goverment people ONLY.