Whisk paprika, thyme, oregano, cayenne pepper, garlic powder, onion powder, white pepper, and black pepper together in a small bowl.
Drain shrimp in a colander for at least 15 minutes. Transfer to a bowl lined with paper towels and dry shrimp for about 3 minutes. Remove paper towels from bowl and season shrimp with 1 teaspoon salt and 1 teaspoon spice blend. Toss to coat shrimp with spice blend.
Heat vegetable oil a large heavy skillet over high heat until oil is smoking hot. Cook shrimp in the hot oil without stirring for 1 minute; stir, and cook 1 minute more.
Transfer shrimp to a large bowl. Let stand until juice forms in bowl. Strain shrimp juices into chicken stock to total 2 cups, adding more chicken stock if necessary.
Melt butter in large skillet over medium heat until butter begins to turn tan at the edges. Saute onion, celery, and green pepper in hot butter until softened, about 5 minutes. Pour in remaining spice blend.
Sprinkle flour into vegetable mixture and saute until combined, 3 to 4 minutes. Stir in tomatoes; cook until tomato juices begin to brown on bottom of pan, about 3 minutes. Whisk stock into vegetable mixture, stirring until smooth. Bring to a simmer and cook until slightly thickened and reduced to a gravy consistency, 3 to 5 minutes. Stir in Worcestershire sauce and hot sauce. Season with salt to taste.
Stir shrimp into etouffee sauce; let simmer until shrimp are cooked all the way through and no longer translucent, about 1 minute.
Garnish with green onions and a dusting of cayenne pepper. Pour over rice in large, shallow bowls.