More pressure is not necessarily better. Peoples brains work differently.

I would never use the app if it posted on facebook, whereas finding people with the same problem who can't embarrass me in front of my friends (because they don't know them) is more useful. Not saying the facebook version wouldn't be useful for some people, but I bet there are also lots of people who wouldnt' touch it with a barge pole. You might want to consider two separate ones.