Try browsing on some of the mailing lists of PA counties. Chester County was a very helpful list with several knowledgeable people. Or if there is a list for Quakers, try looking there. It's been a while since I was on the lists, so I'm not too sure which might be the most helpful. If they were in Philadelphia at some point, then look there. It may take some reading before you find the right list, In my case, I got on the lists and "lurked" for a time. Eventually, I found that my ancestor came on a ship of Mennonites, but that was the result of a clusty.com or google.com search. Try different things. Just don't give up.