Sex slavery does exist, but not so much in the western world. It is more prevalent in developing countries or societies that are in some sort of turmoil that causes the breakdown of social fabric (war, economic depression, etc, etc), mainly because legal protections and enforcement is very weak in those places and those sorts of situations. Typically in that scenario the law is the guy with the gun, so bad things happen, not just sexual and other forms of slavery, many other things as well.
Trafficking on the other hand is widespread, but, contrary to popular belief, does not involve slavery. The media and certain vested interests make out that they are one and the same, but they are not, although obviously on occasion there might be overlap. Most people who are trafficked are in that position voluntarily, for economic reasons, and most pay to be trafficked. Either up front, or in the form of a debt. Usually they rely on the traffickers to facilitate their ability to make money, and for which the trafficker takes a sizable cut. In that sense they are exploited, but they are NOT slaves.