Preheat the smoker or pellet grill to 375–400°F. For a charcoal or gas grill, set up an indirect cooking zone at approximately the same temperature. For the oven method, preheat to 425°F.
Place the panko, egg, finely diced celery, green onions, garlic, ranch seasoning, onion powder, smoked paprika, kosher salt, and black pepper in a large mixing bowl. Stir until evenly combined.
Add the ground chicken and gently mix just until the ingredients are evenly distributed. Do not aggressively knead or overwork the mixture.
Using a small cookie scoop or damp hands, portion the mixture into approximately 18 meatballs, about 1 1/4 inches each.
Arrange the meatballs on a lightly greased grill-safe wire rack positioned over a rimmed sheet pan or on a grill-safe perforated tray, leaving a little space between each meatball.
Place the meatballs in the smoker, pellet grill, or over indirect grill heat.
Cook for approximately 16–20 minutes, checking the internal temperature as they approach doneness. Cooking time will vary with meatball size and actual cooker temperature.
While the meatballs cook, combine the hot sauce, butter, Worcestershire sauce, and garlic powder in a small saucepan over low heat or in a microwave-safe bowl. Heat just until the butter melts, then stir until smooth.
When the meatballs reach approximately 160–162°F internally, remove them briefly from the cooker and toss or brush them generously with the Buffalo butter sauce.
Return the sauced meatballs to the cooker for approximately 2–4 minutes, just until the sauce becomes tacky and the center of the meatballs reaches at least 165°F.
Remove the meatballs from the cooker and rest for approximately 5 minutes.
Toss with a small additional amount of warm Buffalo sauce if you prefer them extra saucy.
Garnish with sliced green onions and optional blue cheese crumbles.
Serve warm with blue cheese dressing, ranch dressing, celery sticks, and carrot sticks.