12/03/2019 and still no small sized stray dogs, I only ever find large dogs and cats 100% of the time. This really bugs me as I like to do pet rescue challenges and all of my spots are only ever filled with large dogs. Hopefully one day EA will notice this and change it.
I linked a picture of a handful of dogs that my Sim has rescued so far. All of them being of a large size and from different areas of the game.