Thanks all of you for the suggestions.
I found this website because for some keywords search he is just under me on the first page of google and then, after an accurate check I saw that a lot of my articles is on this website.
I’ve tried to get in touch with the webmaster but there is no contact form or email. He use hosting from Poland and there is no english or any other language so I don’t know if they will answer me.
I will keep you updated on this matter.
@Michaela15 : I’m not worried about duplicate content penalty, I’m just pissed off that he can reach the first page of google only by copying a lot of articles from other websites (including mine) and stealing me not only the content but even some potential player.