The below links are helpful if you’re looking to move to an apartment that welcomes cats and or dogs.
Zillow Philadelphia pet-friendly page with over 1,500 pet-friendly listings with fair rental price estimates
Trulia Philadelphia apartments page with over 5,000 listings with pet-friendly filters and in-depth neighborhood information
Hotpads Philadelphia apartments page with over 3,000 listings with pet-friendly filters, in-depth photos, information and unique features such as street view of each property
AparmentList Philadelphia A modern website with plenty of filters so you can find a pet friendly apartment.