If you can still see the dog, and it is actively running away from you, then whoop out his name and run in the opposite direction. Keep whooping and running, and generally your dog will turn and chase you down.
If you came out to find that your dog is out of the yard, gone, no where in sight. Call whatever animal control you can and give a description. Find a good picture of him and make flyers, go to supermarkets, stores, vets and ask to pin up your picture. Put an ad in your local paper. List Reward in your ad and on your flyer but do not say how much. Check the animal shelter where strays are brought every day or every other day. Go looking for him, but make sure you have a phone and access to whatever phone number you put on your flyers/ad.
I hope you find your dog. It sucks to lose one, but don't give up hope.
Jenna, RN CGC & Babs, CD RA CGC HIC
Heidi, RA CGC
SG3 Odessa, SchH1, Kkl1, AD
Ninja, RN CGC & Milla, RN CGC
Joy, Star Puppy, RN CGC
Dolly CGC & Bear CGC