I don't know anything about Bangkok....
There are young girls available in our Zona Norte, but for the most part it is not marketed...or if it is it has missed me. I have been offered to buy a BC for $200 over the years...with that you can get your electoral card and then your health card. There are several chicas that have ID that says they are old enough and they will tell you they are.
The bars have young chicas too, but not so many and those chicas don't have health cards....a few clubs get busted from time to time. I've know many chicas that were under age and in the bars sometimes the personnel will tell you. I don't want a reputation for playing with children, but one chica was a really good friend of mine.
She wanted me to take her to dinner, and walking to the car, we got stopped. The officer was telling me I was in big trouble....I asked him what the legal age for dinner is? Anyway I demanded to go to the judge and we did.
Within two minutes the judge said that I was free, that since I met her in a bar, I had to figure she was 18. They brought a doctor in to check her molars...doctor determined she was 18. But the judge was clear...she works in a bar...I can't be charged for a minor...He did not say this, but if I was pimping her then that would be another animal.
Where I would be careful is with walkers....many are 30+ so it is not an issue, but if a chica looks questionable and she is not in a bar or holing up the wall on the side walk I would stay away.
Short story....it exists, but I don't think many people are advertising it. I could be out of the loop on this as I have no interest.