Someone Else's Cat Raises the Stakes, Not the Method
The search itself follows the same shape as for your own cat, but everything about communication is heavier: the cat's owner is deployed, possibly in a different time zone and hard to reach, and the microchip, insurance, and vet arrangements may be in their name rather than yours. Start the same way regardless: search the house completely, room by room, including the outbuildings a nervous guest cat favours, then the garden and the immediate neighbours' ground with their permission. Do this first hour's searching before you make the difficult call, so that when you do call, you can say what has already been checked.
Tell the Owner Early, With Facts, Not Dread
Contact the owner through the channel agreed when the cat was handed over, and if there is a designated family contact at home as well, tell them at the same time. Say when the cat was last seen, which exit was likely used, what you have searched, and what you are doing next. Do not wait hoping the cat returns before the owner hears; owners forgive a lost cat far more readily than silence, and practically, you may need them to confirm chip details, authorise vet treatment if the cat is found injured, or describe a hiding habit from the cat's own home that you would never guess. A guest cat who knows another house may also try to travel toward it, which only the owner can flag.
Log Everything as if You Will Have to Prove It
Because it is not your cat, keep a simple written log from the first hour: times, who searched where, which vets, rescues, and neighbours were called, and any sighting reported. Photograph the notice you post and keep the wording. This log protects the owner, who can see the full effort; it protects you, because memory blurs under stress; and it genuinely improves the search, because a written record stops three helpers searching the same shed while nobody covers the lane behind the houses.
Paperwork You Should Already Be Holding
The time to discover you cannot authorise vet treatment is not at an emergency clinic with an injured cat in a carrier. A well-run temporary placement leaves you, from day one, with the owner's written consent for emergency care, the vet's details, the microchip number, and a named home contact who can act if the owner is unreachable. If any of that is missing in your arrangement, this incident is the prompt to assemble it, and the search log you are keeping becomes part of that same file. Keep the owner's unit or welfare contact in mind as a last resort rather than a first call; the agreed personal channel and the home contact exist precisely so that a missing cat does not become an official notification before the owner hears a calm, factual account from you.
Keep Every Conversation About This Cat in One Place
Messages will arrive from the owner, neighbours, finders, the vet, and the rescue, across several apps, at the worst possible time to be organised. KinsLe Messenger keeps every conversation about a pet in one per-pet communications hub, so the owner's questions, a finder's photo, and the vet's update sit together where you, and the owner when they check in, can follow the whole story without anything buried in a personal inbox.