Some of the suggestions have already been mentioned, but in particular, I think police could have better liaison relationships with community organizations. Of course, that would include the organizations that are represented today, but also sex worker organizations in the community who come in contact with a lot of people who are looking for other services. They could be health services, food, or safe sex supplies. Those groups have contact as well with people who may be in danger for human trafficking.
In Victoria, where I'm located, the police have done a wonderful job to try to increase sexual assault reporting for sex workers in the community. They have done that by connecting closely with different health and social services as well as the local sex worker organization to assign police officers to work with these organizations and to receive training around how to be respectful, non-judgmental, not to use stigmatizing language, and to increase the reporting for all kinds of victimization such as sexual assault, but also if there is human trafficking.
There is a lot that police can do in some jurisdictions. It seems that here in Ottawa, but also in Victoria, the police are making some strides in that way.