Immediately, if you have not already done so, FILE FOR UNEMPLOYMENT INSURANCE. You quit your job, true, but you quit for a valid, employment related reason. There will be fact finding done, if you file a claim. There will be an inquiry. You will tell them what was going on, and why you quit the job, and they will contact the employer, and ask them about the situation. I hope you didn't tell the employer's HR that you "quit for personal reasons." In fact, you should have gone to HR immediately, disregarding what your supervisor told you, as soon as any type of harassment began. Hindsight being very good, of course, there were many better ways to handle this situation.
I agree that it was a very bad thing for you to quit, as of course it did nothing for the case against the sexual harasser and made your personal situation a whole lot worse. But even if you have a job to go to in a day or two, or a week or two, you need to file for unemployment and get this inquiry going. This will help to clarify the situation with whether or not the employee was actually being allowed to harass women on the job. I agree, no matter what they have promised you, these girls he was talking to improperly will never jeopardize their own jobs to the extent of doing someone else a favor. If you are denied benefits initially, and you appeal your unemployment case, you can actually subpoena them for comment in the hearing if you think it will help the appeal.
At your age, I am sure you felt that you needed to be the one to speak up, though you were probably not the target of sexual harassment yourself. But at your age, the fact that you were harassed and pushed into quitting because you spoke up could be some sort of age discrimination situation, particularly when your supervisor told you not to go to HR and then did nothing to help you when the supervisor's harassment began.
After you've filed your claim for unemployment, you may want to have a consult with a labor attorney. If you haven't done so, I suspect one of the first things they'll encourage you to do is file a claim for unemployment. It does flush the answers out of an employer and provide some of the information you may need to go further. But they will never ever determine if illegal harassment occurred or provide you with any damages, or even share their information with the EEOC or any other agency. They'll just determine whether they think you had a valid work related reason to quit the job. And make your former employer realize that you aren't going to just go away quietly. It is not welfare, not income or needs based, and it is not something you put off doing when you've lost a job. It is an insurance program that you need to ask for if you are out of work through no fault of your own, even for a few days.