As an American, the laws in the US apply to all US passport holders, worldwide. Often the Thai cop will demand 100,000 baht, if she is 17, or one million baht, if 16 or under. You do not have it? You are turned over. Many guys end up on planes with an assistant DA dispatched from DC, in handcuffs, facing federal statutory rape charges. Unless you have millions to throw at a lawyer, you are looking at 10 years in a federal pen. And you will be on the sex offender list the rest of your life. America voraciously prosecutes these kinds of crimes and they will throw 5 to $10 million at one single prosecution. Many will dispute this. I have spoken to lawyers about it, and it is correct info. And the US government is over zealous about the underage thing. Not worth it. Always best to check if she looks really young. If she does not have ID, that is real trouble. Do not proceed. The law changed in 2003, when the PROTECT Act was enacted. Prior to that, sex with minors abroad was covered by Customs statutes, which required proof that the US citizen left the US with the intent of having sex with persons under the age of 18 - something that was very difficult to prove. (It's also worth noting that both Jerry Lee and Elvis married teenagers. Laws in the US are peculiar in that many states allow marriage to someone below the age of consent, as long as their parents agree.) Under the PROTECT Act, there is no need for the government to prove intent. If an American has sex with someone under age 18 while in a foreign country, that's a crime, period, even if that sex isn't against the law in the country where it took place.