My dog and his problems with other people

You need to get some profession help from a qualified POSITIVE dog trainer. This is a special case that needs to be handeled with care. Sarah W. (below) has the right idea. Targeting is a wonderful way to help a fearful dog!
He needs help to learn that strangers are not scary. Use conter-conditioning techniques to teach him that strangers make wonderful things happen.
DO NOT under ANY circumstances use punishment or any other kind of aversives with this dog! You will only make it worse!
Also, make sure your dog knows plenty of obedience cues well. Performing commands successfully can help boost his confidence.
Please, seek the help of a professional positive dog trainer. This dog is still living in fear and imagine how horrible that must be. You have been so wonderful to rescue him, with patience and training, you can help him to live a normal, happy doggy life that is not filled with terror over new people.

This is tough because as i understand your frustration you also have to know your dog was abused... this is normal & understandable behavior. I would try putting your dog in more social atmospheres but if he continues to act this way - he just might not be ready... you've obviously been doing okay with whats going on... maybe carry some treats in your pockets and when your dog gets nervous hte people give htem some treats... there is really no real answer to this besides compassion & understanding

ABUSED DOGS ARE NOT HEALED OVERNIGHT. HE FEELS SAFE WITH YOUR FAMILY AND IS TRYING TO PROTECT HIMSELF AND YOU. LET HIM KNOW THAY BEHAVIOR IS NOT TOLERATED. TELL HIM NO AND TRY NOT TO MAKE A BIG DEAL OF IT, BASICLY HAVE THE PERSON COMING INTO YOUR HOUSE IGNORE HIM UNTIL HE IS CALM

Your dog needs socialized in a structured way. Take some time with other people and animals and bring them together in a controlled environment, with everyone acting calmly and purposefully. Interact normally and ignore the dog until he calms down, then praise him and give him a treat. Increase the exposure until he can be around strangers.

The dog whisperer (Cesar Millan) has some really good advice on this particular problem. Check out his web site and I encourage you to get one of his books or videos. Virtually guaranteed to work.

I agree, have the new people in your house completely ignore your dog. Make sure he can leave the room or watch from afar if that's what he wants. If he comes up to someone go ahead and give him a treat but just toss it and leave it at that.

When you have time, work on some clicker training. It can be hard to explain but try this: hold out your hand with a treat on it, when the dog touches your hand to get the treat, click the clicker. Do that a few times. Now hold out your hand without a treat, the dog should sniff it to see if one is there and if he touches your hand click and give a treat. Do this a lot, start moving your hand around, do it with the other hand. Have someone else he's comfortable with come over and do it with them. Then start doing it with people who he usually just watches from afar. He'll eventually get the hint that if he approaches someone and touches their hand he'll get a treat. It takes time and some patience but give it a go for like 5 min a few times a day and he'll get it eventually.

I did this with a shy dog and he figured out if he walked up to random people in petsmart and touched their hands he'd get treats (very food motivated). It was a hoot and it has helped him be less nervous around new people.