My puppy recently ran away, but came back to me a week later (thanks to a craigslist posting)!

Now that he's home, he barks at EVERY. LITTLE. NOISE.

I love my dog very much and he used to be so calm and reposed.

I am sure he is dealing with much anxiety, but how can I get him to stop barking at nothing (literally)?

Glad you got your dog back.

You teach him not to bark by teaching him to bark. Weird, right? But true. Teach him to bark on cue, then he is less likely to bark if no reward is forthcoming.

Also, you can teach him "quiet" by waiting for times when he is quiet and say "good, quiet" and treat.

This is a topic discussed often here so if you need more details, do a search and you should find plenty of advise.

Give a few more days for your dog to adjust and then teach him how to hush.