Skip trace, people search? Need to find owner and tax records NFG

[Troy Sheets]

Looking to contact an owner (or heirs) of a vacant lot. No taxes paid since 2000, it's nearly $12k in arrears (way to go Philadelphia!) and tax records show a different mailing address than the vacant lot. Looked up the owner of the mailing address, call them, and they have no clue who this person is. I've tried a paid website called peoplefinder.com and it's pretty inaccurate. Lists phone numbers and addresses but they're all horribly out of date. 

Are there websites with better info out there? I'm thoroughly disgusted with peoplefinder.com so far. I've tried it out for a half dozen properties and the results are all very outdated. I'm willing to pay for good info, any recommendations?