In a pan over medium heat, cook the bacon until browned and slightly crispy. Remove from the pan and add to the crockpot, leaving as much drippings as possible in the pan.
Add in the onion, celery, and carrots. Season with salt and pepper. Cook until softened and the onion is transparent, about 5-10 minutes. Remove from heat and add to the crockpot.
Into the crockpot with the bacon and veggies, add the clams with juices, diced potatoes, melted butter, chicken stock, salt, pepper, thyme, parsley, bay leaf, and diced tomatoes.
Cook on high for 4 hours or low for 6-8 hours.
Season with salt and pepper if needed. Serve with toppings of your choice.