Do Thai boys define it the same way as we do, that is a boy who provides sex for money? Simple as that.
Someone I know who does sex for money, but has a regular job as a bar manager, got terribly upset and annoyed at the term. Hotly denied he was a money boy! Obviously he isn't a gogo boy but does do sex for baht.
So, to them is a "money-boy" someone who steals money or some other derogatory term that I am not aware of?