My friend and family know. I have a private (as can be) Facebook page with no real name tied to it. I have five Facebook friends most of whom are actually family. I post freely about my PTSD (though not often, but I would and could should I choose), but then my Facebook and yours may be very different.
Personally I think many people won't read this properly or take it on board, but if you're comfortable with the people you know on Facebook knowing then I wouldn't have an issue. But then if someone is going to reject me for having PTSD, then I'd rather them do it sooner than later. I only have space in my life for people I can trust and who can accept me for who and what I am. It may be a little reckless, but I stick by that. Ivd also want to be able to sit in a room with any one (or all) of my so called friends/family with no jumper meaning, some of my self-harm was on display - not because I want to advertise it, but what if it's hot or something like that. I am who and what I am: don't like, it get lost. I don't have the time or space for people who are so judgemental and narrow minded and I certainly don't want to waste my efforts trying to please them by pretending to be something I'm not.
If the whole world knew I had PTSD, it would make my life a lot easier! The world would be a better place if more people were honest and accepting and if mental health issues weren't stigmatised and one way to that is by people being open and upfront.