Knowing and determining your competitors is really important to reach your targeted ranking. It’s part of the technique that one should never miss. Upon searching, I find different tools that would lead you to what you wanted, either for free or with pay.
I always used the http://www.check-domains.com, they do have link tools that will help you in determining your competitors for free.
Google as well is a big help and a friend to everyone. You can freely search for the site to discover where their backlinks come from by just typing “www.+sitename.+com” or just type the keyword:”www.sitename.com”.