Why doesn't Google return search results and how?

A Facebook friend uses two account they request that you use only one, you think this is strange, so you you occasionally check their old account and can clearly see it's still in use. You mention this innocently and they block you, but deny doing this. You don't want to fall out with them but you are suspicious.
So my question; when logged into FB using Google Chrome on a device, a computer for example you cannot find their Facebook account when searching in Google, why? When you search in…

Why doesn't Google return search results and how?