Crypto Currency is legal in Thailand. You can spend it for services and goods as long as the service provider and the supplier mutually agree to accept it.
Please note that you cannot exchange, buy or deposit the Crypto Currency, for instance Bitcoin, at any bank in Thailand. However, you can do so with some companies which have official approval from the Securities and Exchange Commission of Thailand.
In Thailand, we do have the Law concerning ICO ( Initial Coin Offering ) for Crypto Currency.
For your information, a Thai who graduated from John Hopkins University, U.S.A., created Vertcoin, which was ranked No. 4 of the top Crypto Currencies in the world.
This guy also created Zcoin, which is one of the 100 top Crypto Currencies in the world.