Do not run after it. Stay low, turn sideways, look away and use food so that the dog decides to come to you.
The short answer
To catch a scared lost dog, do not chase it, call it loudly or walk straight at it. Sit or crouch sideways, avoid eye contact, toss food on the ground near you and let the dog come closer on its own. If it comes close enough, slip a looped leash over its head rather than grabbing its collar. If it still will not come, leave food, note the time and place, and consider a humane trap through your shelter or a local lost dog group. A frightened dog may run from its own family, so this applies to you too.
Why chasing makes it worse
A frightened dog is reacting rather than thinking. When someone runs toward it, its instinct is to run away, and that often means into traffic. Lost-dog practitioners report that even an owner’s voice may not get through. That is why the default line on a lost dog poster says do not chase, call or text. Tell everyone helping you, and put it on every post. A well-meaning group of neighbors following a dog in their cars can undo days of work and push it into a new area, where you have no sightings at all.
Read the dog first
Look at the body. A tucked tail, ears pinned back, a low body, turning its head away or holding a distance as you move are signs of fear. A friendly dog will often come over on its own and let you touch it, and if it does, you may not need any of this. Do not assume a dog is safe to touch. A frightened dog can bite, particularly if cornered, so never reach over its head or push it into a corner. If it is near a highway, do not approach from the road side, because you may drive it into traffic. Call animal control or the police non-emergency line instead.
Use your body to say you are not a threat
Stop moving. Turn your side to the dog. Look at the ground, not at its eyes. Crouch or sit down. Dog trainers call a set of these gestures calming signals: yawning, slow blinking, looking away and moving in a curve rather than straight on. Drop a piece of food near you, then look busy with something on the ground. Talk softly to yourself, or say nothing. It can feel strange to do nothing while your pet is twenty feet away, but this is usually the best thing you can do. If it edges closer, stay still and drop more food.
Use food and familiar things
Strong-smelling food works best: cooked chicken, hot dogs, sardines or anything your dog loves. Toss it short and to the side, not at the dog, and make a short trail that leads toward you. Try the sound of a treat bag, a familiar squeaky toy or the sound of your car door if your dog loves to ride. Some dogs will get into an open car when they will not approach a person, so open a back door and sit nearby. Bringing a calm, friendly dog that yours knows can also help, if it can be kept on a leash and is safe around strangers.
Securing the dog
Do not grab. A lunge can end in a bite or a dog that bolts for good. Wait until the dog is eating close to you. Use a slip lead, or make one by passing a leash through its own handle to form a loop, and quietly slide it over the head, then let the dog settle. Do not clip a leash to a collar while the dog is pulling back, because it may slip free. Once you have the dog, hold on with both hands and get it into the car before you celebrate.
If it will not come
This is common, so do not see it as failure. Leave food and something that smells of you, write down the time and spot, and walk away slowly. Go back at the same time the next day. Dogs often keep to a route, and a pattern lets you plan. Ask callers to report sightings with the time and direction, not to follow. When a dog settles into a pattern, a humane trap with a local lost dog group or animal control may be the safest choice.
If you are not the owner
Stay in place, note the location, take a photo and call animal control or the number on any local lost dog poster. Check local groups for a matching post. Do not try to catch a dog alone on a busy road. If it comes to you and is calm, offer water, look for tags and take it to a vet or shelter for a free microchip scan. Our post on what to do when you find a dog covers the next steps.
Sources
Whole Dog Journal, How to Catch a Dog on the Loose: whole-dog-journal.com/lifestyle/how-to-catch-a-dog-on-the-loose. These methods come from trainers and lost-dog practitioners rather than formal studies.