I won't lie to you: you are unlikely to keep your job if you're facing sexual harassment in a company that either doesn't have an HR department or doesn't have leadership above your harasser.
If the person who is sexually harassing you is at the very top of the company, you'll have far less protection from retaliation—and far less assurance that anything will be done to help you. Fortunately, if you're fired shortly after reporting sexual harassment, then you may have grounds for a retaliation lawsuit—potentially a far more costly violation of your rights. However, that will still mean you're fired, and that's never a good thing.
What could happen after reporting sexual harassment is you'll be pressured into quitting—either by making your work environment intolerable or by creating situations designed to erode your credibility and create grounds for firing you. It's not fair and it's not right, but it's, unfortunately, one of the ways that small businesses and startups can be difficult places for women to work. Does that mean you have no rights?
By no means. You can still document the harassment, and you can still put yourself in a strong legal position for a lawsuit. You can also file a discrimination charge with the EEOC, or threaten your employer with legal action if something isn't done to help you. Regardless, you'll need to face a hard fact: you'll likely be fired.
If the CEO or founder is the one sexually harassing you, it's more important than ever that you take the situation to the courts—and for that, you'll need an attorney to help you present your case.
The law office of Alan Burton Newman, PLC helps thousands of employees every year hold their bosses and companies accountable for employment violations in Los Angeles. Contact my office–I can review your case for free and tell you what the next move should be.