I have caught plagiarism a few times, and at first I used google but at some point I started using free versions of plagiarism checker that you can find on the web. I don't know if there is much of a difference.
Google gives you raw result and you can only estimate the percent of plagiarism between original and plagiarized post.
With plagiarism checkers, you can have that percentage as well as highlight. Google can be the first step, if I don't find anything, I stop. If I find something, I will use plagiarism checker as the next step