My 16 year old sister was d two weeks ago, what can I do to help her?

Call her local police, inform them of what occurred and the situation that you're in. She'll have to talk to the police about it herself so they can get her side of the story, but since she's still a juvenile, they should have a child protective services advocate and a child expert talking to her so that she wouldn't necessarily have to keep on repeating her story in court, special services advocates are recognized as court experts and can give testimony as to what the victim said. Call the police, give them the recording... just, anything you can. The process will be long and hard, and you will forever want to kill this guy, but you can't do that =(. I know exactly how you feel, when I was younger someone close to me was d as well, and I felt angry and felt like killing the guy, but I got my emotions under control and called the police. This guy's now in prison. Good luck, and I hope the best for you. (Also I'd suggest having the family buy a gun in case if he attempts to make good on his threats of harm... police response isn't always quick enough.)