First, welcome. Then, some questions. What is she doing when she leaves? Mine would run to the mall and shoplift. Compared to some kids, that's actually pretty mild. Is this behavior new or just escalating from when she was younger? Any chance drugs are involved?
If drugs are a factor, you have a whole different set of problems and I'd be looking at rehab if you think it is extreme. No matter what she says, I would insist she get drug tested (no warning on that one), just test her. There are some good ones you can buy but make sure they are for more than just marijuana. Get one that will test for as many types of drugs as possible. If you're pretty sure she's not using, it is something that has to be considered.
Sometimes calling the police can be helpful. A lot depends on their attitude and what programs your police department has in place. I called mine and made an appointment to see a watch commander (not an on-the-street cop, but someone who was at least a lieutenant or higher). The captain I spoke to gave me the options I had with the department. None were really acceptable to me, so I ended up finding an Residential Treatment Center (RTC) for her to go to.
You can make her life as miserable as she is making yours. Remember, the law says you have to provide food, shelter, clothing. No one says what the quality of any of those items has to be -- Goodwill is as good as Hilfiger; a mattress on the floor with a blanket is as acceptable as the canopy bed; rice and peas is really okay. I'm not advocating going to this extreme but there are things she can lose like electronics, especially those in her room. She can find her own way to get to places, no rides or use of car if she drives. (If she drives, that is a privilege I would take away until she shows a lot more maturity and responsibility.) I'd also take away any allowance or financial handouts. She can bring lunch from home and skip the school the food, etc. Basically, let her see what life is like when mom and dad aren't there to give her everything she thinks she needs and deserves. You give those things out of love, you are entitled to respect in return. No respect, no good stuff.
I wish you the best. Teen years are difficult at best. When you have a teen who thinks the rules don't apply to them at all, it goes from difficult to almost impossible.