What excersizes can I do to thicken and firm my buttocks?

Squats. Theres nothing as effective as squats! there are different types of squats! front squats, hack squats, standard squats with barbells! some like to use dumbells and do a varied form called lunges. The point is the gluteus maximus muscle is best stimulated with the sitting and standing motion. If you dont want to use weights do the stairclimber, more effective than stairmaster! hope that helps!
Gluteal Exercises. The muscles of your buttocks are called the gluteal muscles. There are 3 of them (gluteus maximus, medius and minimus.) exercises that help to strengthen the glutes are things like squats and lunges. Exercises can be found here: http://www.Bodybuilding.Com/exercises/list/muscle/selected/glutes.