They are everywhere, it is a human problem, and no respector of person or place. There are whole societies, the one we are fighting in Asia right now for one, that have codified and ritualized child rape. It is part of the human condition that hasn't yet been completely bred out but the good guys are winning! More and more people are acknowledging that children are not simply small adults.

Oddly, some of the same countries are involved in the illegal drug "industry".

All of the mentioned countries have strict laws against csa and prostitution of minors. The reason why they don't proscecute is a combination of poverty, sometimes drugs and above all demand and corruption.
Some of the countries are taking steps because they want to get rid of their bad image. It's a slow process but a start is that these countries have signed the Convention on the Rights of Children, which is binding and obliges them to improve the living conditions and legal rights of minors.
The U.S. and Somalia, btw. are the only two countries who haven't ratified this UN convention.
Some of the prime tourist destinations have started to work with police in European countries, so that perpetrators can be proscecuted (sometimes in their country of origin).

This is a gross exageration and stereotype. I don't know how much you know about every single society in Asia and what country you are fighting there, but people are a lot more decent than we think. Having learned a lot about csa I would also dare to say, that we've got plenty of perverts in the homeland.