I haven't done it, but I have looked at it. There's 10+ miles of trail from Bowerston to Jewett (http://www.traillink.com/trail/conot...eek-trail.aspx), which should be about 20 miles of road riding from New Phillie. Another 30 miles on the road to Steubenville/Weirton where a trail picks up to take you right in to the Pittsburgh network (http://www.traillink.com/trail/panhandle-trail.aspx).
While I haven't biked around New Philadelphia in years and years, I would guess that any route you found from there to Bowerston would be decent. It's all country roads, I believe. The only part that might require input/planning is Jewett to Weirton. The more straightforward roads look bigger, and probably options to cross Ohio are limited and of varying degrees of safety. But 50 on-road miles from one trail to the other doesn't sound bad. Although that's a full day's riding for lots of folks, and I have no clue about overnight options at either end of that trip.