I tried one day with an amazing sexy girl from Ukrania (porno style girl), she kept talkint to me about 5 mins while walking on a high street. I asked her if I could invite her for dinner and she said "no, I have boyfriend", but when I suggested she worked as "Model" in flat with other girls, she got really upset with me.
So it is very difficult in street to approach a working girl, but I can guarantee you that in Night Club its really much easy, specially student girls that used this way of making money.
Regards.