Always bring along some treats and the squeaker from a squeaky toy to the dog run. Pay close attention to your dog. When he's not interacting with other dogs, or not sniffing around, and seems to need something to do, make a kissing sound or squeak the squeaker. (If I'm in a big dog run I'll use a ref's whistle.) When he looks at you, show him that you've got a treat, waving it enticingly. But don't call him to you yet! Wait until he starts running toward you. Then, while he's already in the process of coming, say "Muttsy, come!" in an excited voice. Then reward him with the treat and a lot of praise. It wouldn't be a bad idea to get him to chase you around a little too. This may excite not only your dog but several other dogs in the vicinity, so let things settle down a little, let the dogs will start playing again, then wait until there's another lull in the action, and repeat.
Another cool trick is to play a modified version of "hide-n-seek:" when your dog isn't paying attention to you, move. Go stand or sit somewhere else. Then when he looks back to where you were, he'll suddenly have a strong desire to find you. When he does see you, wave a treat and run away. He'll come flying toward you as fast as he can. As he does, say, "Muttsy, come!" in an excited voice, then reward him with the treat and a little bit of chase. (Most dog runs frown on people getting dogs to chase them around like this, so you have to keep it to minimum.)
After a few days of doing these exercises, your dog will automatically start looking for you more often when there's a lull in the action. He'll even start coming back to you on his own, just to check in with you from time to time. It's vitally important during this stage, that every time he comes back to you on his own, without any direction from you, that you praise him and give him a tasty treat.
One other important bit of advice, if your dog is in the habit of running away when it's time to leave the run and go home, never stand there with the leash in your hand and call him! Have the leash hidden, and put it on your dog while he's distracted by eating a treat out of your hand. Another good tip: after you leash him up, take him for a brisk walk, a game of chase and tug, while running or jogging around or near the dog run. Then take him back inside and let him loose again.
If your dog has as much fun playing with you as he does with the other dogs, you may find that when you get back inside the dog run he'll actually hang around you for a while before he finally runs off and throws himself into the tumble of dogs waiting for him. If you do these exercises often enough, and make your dog's experience of leaving the run with you as fun for him as being inside with the other dogs, he won't associate the leash with the feeling that "the fun is over." And the really cool thing is, after just a few weeks of playing with him, you can simply show him the leash and he'll come running over to you to be leashed up. You won't need to keep doing this every day, either. Nor will you have to keep giving him treats every time he comes (you should gradually wean him off the treats altogether anyway; they're just a tool for those initial stages of learning).