If he or she is a Thai national only holding a Thai passport, then he or she would need a visa.
It is different for us going to Thailand, as we can get the 30 day visa at the airport. Plenty of info on this forum, just do some searching and you will find it, especially in the "Relationships with Thai girls or bargirls" section
http://www.phuket-info.com/forums/re...irls-bargirls/