Copyscape is the best website for plagiarizm checking. To check whether your content is roaming somewhere on internet with different name then just enter the URL of your site. The copyscape will search the whole webpages that has been indexed for google search.
The result will be given in few seconds, whether your parts of content is plagiarized or full.
There are two other services on Copyscape, one is Copyscape Premium and other is Copysentry. While premium allows to check plagiarizm offline by checking copy and pastes of web address, Copysentry checks round the clock and will inform you instantly when someone is plagiarzing your content.