Many teachers often want a classic five-paragraph essay, so it often helps to create a thesis that has three main points. A thesis should present a defendable position, and you will support this position with evidence in the body paragraphs of your essay.
There are numerous angles that you could use to examine the topic of human trafficking. You could examine exactly who is exploited with a thesis that looks something like this:
Human trafficking exploits children by forcing them into commercial sex, victimizes adults who are forced to various laborious work, and abuses children and adults who are forced to work to repay debts.
Those three key points will become your three body paragraphs. In each, you will provide more information about each of those groups, including data to show how and where this happens across the world.
You might also consider the effects of human trafficking on society. That thesis might look something like this:
Human trafficking has devastating effects on society, including the devaluation of women in societies, the decreased physical and mental health among those who are trafficked, and an increased population of organized criminal groups.
You might also examine which populations are most at risk of being trafficked:
Human trafficking targets some populations with greater frequency, including the poor, the socially excluded, and the weak.
You could then provide research that demonstrates how each of these groups becomes more vulnerable to human traffickers and conclude with strategies that societies can employ to protect its most vulnerable members.
I hope this gives you some ideas as you construct a thesis regarding this worthwhile topic. Good luck!