@iowaike,
I would say that anyone you've ever laid eyes on, whether your eyes met, or you just saw them doing something that didn't include you. I say this, because your subconscious mind remembers every sight and sound you ever experience, even if you don't recall it. Therefore, if you want to talk in these terms, I would say millions. Think of all the events you have attended where there were hundreds or thousands of people. If you saw their face, whether they saw you back, I would count that as having run across these persons. If you must have a conversation with them, or you've watched them make a presentation, but never spoke to them, then the numbers would be less. Hope my idea helps.