Get the tortoise contained, calm and out of trouble
A found tortoise's first need is simple security. Put it in a sturdy box with sides too high to climb, a spare storage crate, or an empty enclosure if you keep reptiles yourself, and line the base with newspaper or old towels rather than soil you know nothing about. Tortoises are stronger and better climbers than they look, and a half-hearted container just gives you a second lost tortoise to worry about. Place the box somewhere quiet, shaded and away from dogs, cats and curious children, then leave the animal alone to settle. Skip baths, handling sessions and introductions to your own pets: to a tortoise that has just been picked up by a giant stranger, every extra interaction is stress, and stress is the main thing you are trying to spare it.
Offer water and familiar greens, not a feast
Set down a shallow, heavy dish of clean water, low enough that the tortoise can step in and out and rest its chin at the rim without tipping. Many found tortoises are more thirsty than hungry after time outdoors, and a long drink or soak in the dish is often the first thing they choose. For food, offer plain leafy greens such as dandelion leaves from an unsprayed patch of garden, romaine or other salad leaves, and a few edible weeds or flowers if you can identify them confidently. Avoid fruit, bread, dog or cat food and anything seasoned, and do not worry about a perfect diet: this is short-term hospitality measured in days, and hydration, warmth and calm matter far more than a balanced menu.
Record the details that prove who owns this tortoise
Photograph the shell from directly above and from both sides in natural light, plus any distinctive marks, old injuries or unusual shell growth. That shell pattern is effectively the tortoise's fingerprint, and it lets you check a claim properly instead of handing the animal to anyone who simply says it is theirs. Write down where the tortoise was found, the time, and what it was doing, because owners searching a neighbourhood think in exactly those terms. Ask anyone claiming the tortoise to describe those markings or produce their own photos before you arrange a handover, and keep the animal's location out of public posts for the same reason.
Check the places an owner would look first
Check the missing-pet posts for your area, tell nearby veterinary practices and reptile rescues that you have the tortoise, and put a plain found notice where local pet owners will see it, describing the species and area without the identifying details you are holding back. Tortoises rarely travel far under their own power, so the owner is very likely within a few streets of where the animal was found. If nobody comes forward after a genuine search, a reptile rescue can hold the tortoise while the search continues. While you search, KinsLe's Lost Pet Alert System adds a listing for this animal at no charge within your profile, shows that listing on its map view, and allows whoever lost it to send you a direct message.