It's your pregnancy. Your happy time. You have the right to share it on facebook and with the people you love. If these people are truly your friends they'll be happy for you. Even if it hurts at first. they most definitely won't begrudge you.
Also P.S I had a MMC in December I was 12.5 weeks. I've had a few pregnancy announcements on my facebook. I am happy for each and every one of them
I really think it's a personal and individual thing. Some can handle it better than others. So if someone has to disappear for a bit, I don't think that they aren't true friends.
I was dying inside (2 losses prior to DD) every time. Some days it felt like pregnancy was thrown in my face. It was a very confusing time as I was happy for the people in my life, but at the same time it was killing me.
I always did my best to be happy and support them, but I also had to take care of me, so I had to set boundaries. I will say I avoided baby showers like the plague. There was just no way I could get through it. I still did something in my own way for them, but I couldn't go to the shower. For my friend, I just drove to visit her (with a gift - 3 hour round trip) and spent some one on one time with her. My SIL, I made her baby shower cake.
So I think it's really a personal thing. Everyone handles their losses and ttc issues differently. It doesn't mean that they don't care. It just means that they are doing what they have to do to take care of themselves, even if it's setting boundaries.
The OP should definitely be happy and excited about her pregnancy, but I think if her friends need some time away, it doesn't mean that they aren't true friends; it just means they to set boundaries so that they can take care of themselves (as long as they aren't tearing OP down in the meantime).