Combine cream cheese and butter in a large bowl. Beat with a mixer at high speed until well blended. Add sugar; beat until fluffy. Add vanilla, egg whites, and egg; beat well.
Lightly spoon flour into dry measuring cups; level with a knife. Combine flour, baking powder, baking soda, and salt. With mixer on low speed, add the flour mixture and buttermilk to cream cheese mixture, beginning and ending with flour mixture.
Gently fold in raspberries and walnuts.
Place 24 foil cup liners in muffin cups.
Spoon batter evenly into liners.
Bake at 350° 25 minutes or until a wooden pick inserted in center comes out clean.