I have dealt with these cases for over 10 years in federal court, and have never seen an anti-trafficking approach that targets the end users in investigations. That is the equivalent of trying to take down the Chapos in drug trafficking by arresting and publicizing the arrests of drug users/possessors at the street level. You might claim some incidental end user deterrent (take out the demand by targeting end users, kill the business profits and then the business), but I believe we have established through rising crime rates that the approach is not generally effective in trafficking type offenses (drug, human, alien, etc.).
In trafficking generally, that approach would alert the leader/organizers at every level to active law enforcement interest (we may assume they are not in custody because they aren't morons). Add to that the end users likely face small punishments, are unlikely to know anything of the actual operation, and even if they have some knowledge are unlikely to snitch and face possible violent reprisal given the risk/reward calculus for a trivial offense.
Law enforcement/prosecutors can make use of the low level leaders and organizers in human trafficking activities. Charges having as elements coercion or threats tend to carry serious prison time in federal court, and defendants will possibly inform on the organization to save themselves. These operations are frequently interstate or international, so the odds of some local operation successfully conducting that type of investigation is small at best. The odds of someone cooperating when local clowns go public is about zero, as twenty years of prison time is better than 5 minutes on the street before the unknowns of the international operation take you out as they will be watching the public proceedings and sentencing (i.e., extremely lenient sentence means snitch).
Local cops take down brothels all the time. Those are frequently RICO-type cases (forfeiture and higher sentences) because of the illegal proceeds/activity controlled through an organized structure rather than, for example, the independent street walker. Brothels, when populated by prostitutes who voluntarily join and participate in the operation, do not implicate human trafficking by definition.
Victims will testify in trafficking cases. In the international cases, the incentive is lawful status here (U-visas). In interstate cases, the feds will take every named defendant down and send them away for a long time, so the threat is eliminated to the witnesses. Federal indictments generally stay sealed until the majority or all of the co-conspirators are arrested, with pretrial release a statistical unlikelihood.
