If peanut butter is thick, microwave for 10 seconds or until warmed through. Peanut butter that is loose in consistency may not need to be heated.
With an electric mixer, blend cream cheese and peanut butter until combined.
Add powdered sugar and vanilla, beating until smooth.
Fold in Reeses Peanut Butter Cups.
Line a small bowl with plastic wrap. Spoon peanut butter mixture into the bowl over the plastic wrap. Fold plastic wrap over peanut butter mixture and refrigerate until firm, at least 1 hour.
When ready to serve, open plastic wrap and flip peanut butter ball onto a platter. Remove plastic wrap. Cover the peanut butter ball with Reeses Pieces candies.
Allow to soften slightly and serve with graham crackers, pretzels, cookie wafers, apple slices, etc.