This is obviously a very emotive issue and it's easy for discussions like this to get out of hand. From what I know of the regular posters here no one would mean to imply that another poster would engage in any such behaviour.
I think responsibility is a key point here. Yes, there is a difference between a scared 9 year-old being forced by an adult and a 13 or 14 year-old aware of their own sexuality doing the running; however, just because something is on a plate you don't have to eat. I had a friend at school who at 13 was already very promiscuous, probably due in new small amount to a lack of live from her parents who used her as a weapon in their messy divorce. She absolutely believed she knew what she was doing when she chased these men - until she ended up having to go to the doctor with our form tutor for a pregnancy test. She very quickly became a scared little girl again after that. She could certainly have passed for 16, but I have to wonder how many questions the men involved were asking.
Of course it's not just girls. I was once contacted by a young man on a social networking site who'd found we through a group and wanted to be 'friends'. His profile said he was 18 - it was only once he'd told me in fairly graphic detail what he wanted from our friendship that he admitted he was only 16 but 'liked older men'. He was clearly the one doing the chasing here, but I had a choice, and I felt a 16 year-old might regret this kind of behaviour later on; plus if he'd already lied once, how was I to know he wouldn't have said 'well actually I'm not quite 16 yet...' once it was too late to stop me breaking the law? I owed it to myself to be careful and to him not to take advantage, even if as far as I knew it was all legal.
