I'd say pretty much all of them are aware of this place. If they don't find it themselves, someone in their surrounding will surely come across it sooner or later. But I know a few models who consciously avoid reading their threads, though their family and friends check it all the time.
Working as a model means being in the spotlight, though, and you can't be too sensitive. Yes, most of them ar far from celebrity status, and many of them are very young, but being famous, even if it's in a very limited fashion (no pun intended) always means random strangers will make jealous/thoughtless/mean comments about you.
It's not like anyone's forcing them to visit tFS or similar sites, and this is just a discussion forum on the Internet after all, not much discussion happening if people cannot express negative opinions as well. But there are decent ways to do so. "She's not my type", "I find her way too common", "her lack of expression really bothers me" or "she really needs to work on her walk" are hardly offensive comments. Possibly hurtful, but it's just opinions from complete strangers with nothing better to do, and if you can't handle that, then you're definitely in the wrong business.
But, I'll never understand people calling a girl hideous, fugly, or deformed (I actually saw someone make a comment like that - huh?). Not only is it mean and petty and weird - what happened to a good old "I don't get her appeal because she doesn't know how to pose, and I don't find her attractive either" - but it also makes absolutely no sense. They are models after all...