If you live in Thailand for more than 180 days in a calendar year, then you are liable for Thai taxes and are considered a Thai resident.  Residents are required by law to file taxes on all income – including income earned while in Thailand, whether that income came from within Thailand or from foreign entities.  If you live in Thailand less than 180 days in a calendar year,you still must file a tax return.  But your tax liability will only be on income received from within Thailand.

Americans living in Thailand and earning less than $70,000 are exempt from paying U.S. income tax.  However, a tax return must be filed yearly in order to retain your social security rights. 

It is always wise to find an accountant and an attorney who live in your newly adopted country and speak your language.  You will avoid complications with the local laws and probably save yourself money.