Make prostitution legal and well regulated. You'll decrease the demand for sex slaves. Anyone who claims to care about sex slavery and doesn't advocate the legalization of prostitution is simply not serious.
Sex slavery is a much worse problem than what is shown in Hollywood films. It's not limited to cute 20-something girls being forced to service powerful executives in posh locations. The majority of these sex slaves are children, drugged and kept prisoners in slums and secure houses. Do you want to legalize child prostitution and child porn, too?