The following is meant only as a general guide, as situations vary tremendously. Personal safety should always be considered. You should contact Animal Control Officers, Shelter or Rescue people in your area for advice and options, especially if you are unable to attempt luring.
Be Ready
Be prepared to attempt a rescue if you see the dog. Searchers should always carry a leash and basic bait food like hot dogs, string cheese, meatballs, stinky cheese like Provolone or Swiss, salmon flavored kitty treats, luncheon meats, and small tubs of food with foil peel-back tops such as Little Caesar (dog) and Sheeba (cat) that can be easily carried. Bring a squeaky toy, ball or Frisbee if your dog likes them. Bring extra clothes if you plan to be out for any length of time. Lost dogs generally respond better to rescue attempts made by women. They might prefer children they know and love rather than the adult owners. Children must be old enough to understand the situation and remain calm.
Luring
The object of luring is to get a dog to overcome its' fear, trust you, and approach for the food. To accomplish this you should assume a non-threatening position on the ground below the dog's eye level. If several people respond to a sighting, only one should attempt to lure the dog and another can be a backup. The backup should lie on the ground, far behind or off to side of the lead person, but still within a reasonable distance. The backup should discreetly keep an eye on the dog in case it bolts so you'll know what direction it headed. A backup may start or finish a rescue attempt if the other person did not succeed. A two person rescue can be more stressful for the dog as it will watch both people. Make sure it only needs to concentrate on one. Do not have noisy groups of searchers walking or running around a sighting area. Dogs can sense when they are being hunted and can easily outmaneuver the best of you. Organize everyone and have a plan, who to call and what to do, if the dog is spotted. Time is always critical and a quick response is best.
Quiet Patience
Remain calm and focused when responding to a sighting area. Don't slam doors or shout. NEVER CHASE. Don't make any sudden movements and keep arms close to your body. Do everything slowly or the dog may bolt. Approach a dog from the side, never head-on. You have to get as close as possible without alarming it. Observe the dog's body language but don't stare. Staring is what predators do to their prey. How close you should get depends on the dog itself and where it is. Out in the open, give them wide berth. In tighter areas you could probably get closer, about 60 feet or so. Slowly kneel to the ground, talking softly and reassuringly. Use words the dog may know. Cookie? Have food ready and position yourself flat on the ground. If you have a toy, set it beside you as an extra incentive, but hunger is usually the primary driver that makes dogs abandon caution. Don't smile which is baring your teeth in dog language. Gently toss bits of food towards the dog, keep talking and act submissive. Close your eyes, bow your head and turn it to the side a few times. Try pretending you are enjoying the food (yummy... pretty good stuff!) then share by tossing bits closer towards you. A dog may take a bit and retreat or move closer. Praise all forward movements. This could take up to/over an hour. BE PATIENT - DO NOT RUN OUT OF FOOD! Toss small thumbnail size pieces.
To grab, or use a gentle hand?
When the dog is less than an arm's length away, you have to decide what will work best, a gentle hand or quick grab. If the dog is at ease, try petting it under the chin. Gently grasp the collar and attach a leash. If there is no collar, discreetly slip a leash over its neck. If the dog is overly cautious or the situation demands immediate rescue, just think positive, focus and make it happen. You will have to grab the collar, neck, fur, whatever, hang on and quickly get a leash on it. Be aware that collars loose from weight loss are easier to locate and grab, but the dog can also slip out of it very quickly. Hold on to loose collars!