Add the chicken breasts to the slow cooker.
Pour in the chicken broth and buffalo sauce.
Add the cream cheese cubes, diced celery, garlic powder, salt, and black pepper.
Cover and cook on low for 6 hours.
Remove the chicken breasts, shred them with two forks, and return the meat to the slow cooker. Stir until everything is combined.
Ladle the soup into bowls and finish with crumbled blue cheese and sliced green onions.