Hi tgirl, I'm sorry you are in this situation. It's horrible, isn't it? Quite a few of us here have had this experience; if you use the 'advance search' feature (top right) and search for words like 'violence', you will find previous threads and lots of advice...
You have a right to feel safe and be safe in your own home. Teenagers get to a point where you can't control them, and if they can't control themselves, then you need to get help to make sure you stay safe.
I am glad he hasn't actually hit you. But smashing things and threatening you are illegal too, as well as being really unpleasant. You need to draw the line, since he can't do it himself, and tell him clearly that all violence and intimidation needs to stop. Tell him you will call the police if he threatens you or hurts you or breaks anything - and then if he does, follow through and call 999.
The police will come, and they will take you seriously. They will warn your son, and ask you if you want him arrested. Often, it only takes one 999 call for teens to realise you are serious, and to jolt them into taking control of their actions. For me, it took 3 calls, and the third time I had him arrested and charged. It was awful, but it was better than continuing to live with violence and fear - for him as well as me and his bro.
The other thing you may want to consider is whether his violent outbursts are linked to drug or alcohol misuse. Skunk (a modified form of cannabis) and m-cat/mephedrone are widely available, being taken by many teens, and IME cause aggression and loss of control. If you suspect he's taking drugs, then you may not be able to stop him, but knowing it will help you avoid 'flashpoints' and stay safe. Monday mornings were bad for us, for instance.
I felt like I had entered a strange, nightmare-ish parallel universe when all this started happening in my family. Violence by teens towards their parents is pretty taboo, so no-one talks about it much. But it's more common than you think, and you can take action. You're not as helpless as you perhaps feel right now. And people here can support you...