If you're looking for a meeting place or a good stop around ½ or halfway between Myrtle Beach and Pittsburgh, you can try Bluefield, VA, which is about 5 hours northwest of Myrtle Beach, or about 5 hours south of Pittsburgh.
Other possible places to stop near the midpoint include Fancy Gap, Pulaski, Crockett, and Bluefield.
About ¼ or a fourth of the way, you can stop at High Point, NC. This is about 3 hours north of Myrtle Beach.
About ⅓ or a third of the way, you can stop at Greensboro, NC. This is about 3 hours north of Myrtle Beach.
About ⅔ or two thirds of the way, you can stop at Elliot, WV. This is about 6½ hours north of Myrtle Beach, or about 3½ hours south of Pittsburgh.
About ¾ or three fourths of the way, you can stop at Widen, WV. This is about 7 hours north of Myrtle Beach, or almost 3 hours south of Pittsburgh.
If you drive straight through without stopping at all, the total distance is 610 miles. The distances shown above don't include local roads to get into each town, so if you're planning a long road trip, make sure you factor in traffic and road conditions, rest stop breaks, and interesting detours along the way. If you're in a rush, you can do the trip with zero stops, and your total travel time would be around 9 hours, 56 minutes.