communicating with your boss through facebook

Yes, but there is a difference between reading something on FB versus seeing for yourself. If someone was majorly upset on FB, they will probably seem upset the next day, it's more appropriate to ask how they're doing based on their demeanor instead of referencing FB.

There should be a clear defining line of professionalism, with a human side, which means that: If I see my boss crying I will ask him if everything is alright, not based on what he wrote online 12 hours ago.