The best way to do it, is to start a company in Thailand.
Then you can buy the properties under the name of the company and rent them as AirBnB as you wish.
But we also know quite a few people who have just rented homes and condos and just re-rented them as Airbnb and make the profit. They never bought any units.
So might be a good way to test the waters first without putting down money. Then when you perfect the business model, you can go ahead and buy units.
The real-estate market in Bangkok is crowded and cut-throat and is a buyer's market. So find a good way to test the waters first so you don't lose a lot of money!