Search file duplicates in OSX by hash
You might also use fdupes. It doesn't have an option to search for duplicates of a specific file, but you can just grep the output for the filename:

fdupes -r1 .|grep filename


-r recurses into directories and -1 prints each group of duplicate files on a single line.

Other useful examples:

fdupes -r .  finds all duplicate files under the current directory;

fdupes -r . -dN  deletes all except the first duplicate from each group of duplicates;

fdupes -r dir1 dir2|grep dir1/|xargs rm removes duplicates in dir1.

You can install fdupes with brew install fdupes.