I tried to post before, but lsot it.
Currently no trails that go all the way to Mo-town.
The Sheepskin trail , off the GAP past Connellesville will eventually go 32 miles to link with Morgantowns North Mon Trail. Currenlty the Sheepskin Trail only goes two miles.
http://www.dunbarhistoricalsociety.com/Trail/trail01.htm
You could take PA Bike Rt A to the WV border, then Rt 19 or WV Rt 100 the rest of the way.
ftp://ftp.dot.state.pa.us/public/pdf/bikes/state_map A.pdf.
There's a rail trail along the Mon for 5 or 6 miles near Rices landing, PA. I don't think there are plans to link it up with anything else.
I did a trip to Morgantown in April and reported it here in enough detail to get complaints about the length.
http://bike-pgh.org/bbpress/topic/round-trip-to-morgantown
Mick