"They could, if the person who they are looking up is an idiot."
There are more of those than you would think.
Of course that means that anyone that you would like to find you cannot find you either and this raises the conundrum that all security and privacy faces, simply put;
Engagement Surface = Attack Surface
So to a company that wishes to engage and interact with it's customers it must increase it's engagement surface, which opens itself up to attack. The same principle holds true for individual privacy...if you wish to remain totally anonymous, then burn your computer and move to an isolated shack in the bush and speak to no one.