The operative word here is "knowingly." Even fairly knowledgeable parents can't keep track of everything a teenager does every waking moment of the day, unless they are going to follow her around 24-7. This does not mean that they are too busy, don't care, or are off making money. Even if they ban such sites from their own home, kids can access sites like that at their friends' houses, at the library, or any other place where one can connect to the Internet.
I think that a lot of it is fake. I tried the zipcode thing and it pulled up about 30 'cute young chicks' that say they live in a neighboring town....
Yet the entire population of that town including the ranches out to about 10 miles away is only about seventy people total, and very few of them are "Teens to Twenties females".