Combine raspberries and sugar in a medium bowl. Let stand 5 minutes, stirring occasionally.
Place yogurt in another bowl; gently fold in whipped topping until combined.
Layer about 1/3 cup each angel food cake, raspberry mixture, and yogurt mixture in each of 4 stemmed glasses. Repeat procedure once. Garnish with additional raspberries, if desired. Serve immediately, or chill until ready to serve.