For many rescues that were found dogs which also show signs of neglect or abuse, this behaviour is rather common. They seem withdrawn and because he may not have been given the 'priviledge' or 'opportunity' to live with loving people, he may be confused that now he is welcomed. Most dogs that have such signs as yours were probably not given the time of day and shoved aside. If this is the case, then all this will work out in due time.
I have had MANY rescues like this including dogs that have been severely abused. The best thing to do is to let the dog come to you on his time. Once I get one of these dogs into my home, I ignore them and let them experience or view the interactions that I have with my other animals. They will pick up pretty quickly and will want to participate with you and the others. I also do not speak to them at all for a few days. If I need to correct a behaviour, I do it non verbally, and usually just click my fingers and point to what I want from them (such as go lie down, down or off). It sounds harsh but it really is not. I know your first instinct (as mine) is to love them up and let them know everything is ok. In doing so, sometimes it over stimulates them or confuses them as they do not understand our gesture of kindness and affection.
To entice play, I usually take a ball, throw it and run after it myself (that is if I do not have other dogs to teach the dog how to play). The dog will eventually want to join in with the excitement and curiousity to engage in the fun.
As for food, I would place the food down and walk away. Let the dog explore the food and decide to take a nibble. Try adding some plain yogurt to the food or maybe a raw piece of meat. Remember however not to mix raw with kibble food. You can also try adding maybe some beef broth to see if that will spark curiousity and get his hunger going.
I am certain that others here can assist with some ideas as well. There is a training expert here called TenderFoot and she packed with ideas and methods. Hopefully she can assist you.
Best of luck to you and I just wanted to say thanks for considering a rescued animal. There is nothing quite like the bond you will eventually have with your new canine...they know who saved them!
Take care and keep us updated on progress please. So nice to meet you.
