What do I do if the reporting party is a non-employee during a workplace investigation?

What do you do when the complaining party is not an employee? The same thing that you do anyway. So, you investigate those complaints because it doesn't matter who makes the complaint. You as an employer are now on notice that you have a harasser, discriminator, or bad actor in your employment. And that is what actually triggered the obligation to look into something. It's not noticed that you have a victim. It's noticed that you have a bad actor that triggers title seven in the other state law and other ADEA-type investigation obligations. So, it doesn't matter who the complaining party is. If you are put on notice that you have about actors in your workforce, you need to investigate it regardless of who that reporting party is.