I like the idea. Plenty of people everywhere keep an eye out for strays, and having an app to connect them would be valuable. The main issue is how to let them know that the app exists.

Where I live, a slightly similar app (intended to connect lost pets with their owners) has found widespread local adoption. It is promoted by a local non-profit, so maybe partnerships with non-profits would allow you to find the audience that will appreciate something like this.

Also, this needs an Android app. You need every user you can get to make it successful.