If you are considering visitng Thailand then it is always best to apply for a Thai tourist visa. The reasons are sound and here is why you need a Thai tourist visa.
This visa allows you to stay in Thailand for 60 days and can be extended for another 30 days at immigration for an additional 1,900 Baht. If you are going to backpack in Asia then you will only receive 15 days in Thailand when you cross the Thai/Cambodian border. This has been an issue for many years and Thai Immigration has cracked down on visa on arrival abusers. Ensure that you have your tourist visa when you cross the border if you plan to stay in Thailand for longer than the 15 days.
If you arrived in Thailand and found employment, your tourist visa can be converted to non-immigrant B visa so you can apply for a work permit in Thailand. It does take 4 weeks or a month to do the conversion so if you are already on an additional 30 extension then it might be better to leave the country to obtain a Thai “B” Visa or business visa. There are options, however the tourist visa is very limited in scope. Take note that having a tourist visa or business visa alone is not enough for your to work in Thailand. You need to have a valid work permit. Even volunteer work also needs a work permit.