Ah, well you don’t need a special app for that, just a phone. People searching for their lost pet put their contact info out as widely as they can so it’s very easy to find all over the place on social media.
This scam is unfortunately very common in real life, though it’s not set up as a mugging. They’ll demand a reward (they wont have the animal of course, though they may have a sorta similar picture to send you, or a fuzzy one.)