Use Copyscape To Detect plagiarism
Copyscape is one of the most popular online duplicate content detection tool. To check plagiarized content just enter you website/blog url and press go button. It will show you the list of website who copied you content partially or fully.
Copyscape available both in free and premium version. Free version of Copyscape provides only limited set of functionality. The Copyscape premium version provides more advanced features such as Batch search and checking offline content.
Use Blekko to Detect Duplicate Content
Blekko is basically a search engine but it is also good Plagiarism detection tool. To detect duplicate content using Blekko just enter your website url and after this add domainduptext or duptext.
It will detect duplicate content for your entire domain.
To use for individual url
Plagtracker and PlagSpotter To Check plagiarism
Plagtracker and PlagSpotter other excellent tools to know who are copying from your website.It shows copied content through highlighted text.
Like Copyscape it also available in free and a premium model. The premium version is 3x faster and loaded with more advanced features.
plagiarism-checker.me is another awesome Plagiarism checker tool. You can paste the text on the dialog box they provide or upload the file to check for copying website.