I'm familiar with West Philly but don't personally know any squatters. I can't afford rent though I have a job.
Gentrification killed a lot of cool places. Hangout downtown you'll run into some folks. (North East corner of Rittenhouse is still a popular place for fixed gear kids, punks, travellers) There is a couple places in North Philly and neighborhoods above that. Honestly it's nice enough to live outside from now until October in Philadelphia. I think some of my old friends still have a spot way down south but I do not know anymore.
Drugs ruined a lot of good bandos because they are just glorified shooting galleries now, especially the farther north you go from center city.
They're doing so much construction in town now it's crazy how much it has changed. The local colleges own so much property and want it to be developed. However, that means plenty of construction sites to dwell in. (This is honestly your best bet) You could sleep downtown rather comfortably in some of these construction sites.