Sick of my sister getting away with everything?

My parents are huge pushovers. My sister is just about to finish her grade nine year, her first year of high school. So far this year she has come home drunk (to the point of throwing up; she was completely smashed), pierced her belly button illegally (going to a sketchy tattoo parlour and telling them she was 16), sneaked out of the house, been late for over 50 classes, and just today she got caught shoplifting with a friend. My parents know about all these things, and other than getting angry occasionally, they don't do anything. They say that they don't want to start a war, and I get the feeling that they don't want to be the "bad guys". They insist she's a good kid, but behaviour like this just keeps occurring. I'm seventeen, and I'm so sick of sitting here and watching my fourteen-year-old sister keep spiralling downward. She's smart, but isn't doing very well in her classes. She doesn't care about what I have to say, and my parents just don't do anything. Even though the police called today and they had to pick her up from the store where she shoplifted, they still don't do anything. My parents aren't bad parents; they raised my older sister and I to become very successful. But I'm so sick of them not doing anything. Has anyone ever been in a situation like this, or have anything to say? I'm so frustrated right now.