Looking at the statistics produced by TAT
http://www.tat.or.th/stat/index.html and assuming that
1) Most people coming on business are men.
2) The excess of males over females is represented by sex tourists
I would say that there are about 700,000 sex tourists coming to Thailand
each year i.e. 8% of the tourist industry.
This might overstate the number because most countries, not necessarily sex
tourist destinations, have an excess of male over female tourists. However
this is balanced out by the fact that
1) Some of the business delegates are be women
2) Some women may be sex tourists.
Which ever way you look at it, sex tourism is not where the money is as far
as the tourist industry is concerned.