Kiesewetter committed to Penn State just two days after receiving an offer.
Buddin finished his Penn State career with 12 total tackles and a fumble recovery.
Black runs a 4.25 40-yard dash, according to his Twitter profile.
Hagans returned to his alma mater, Virginia, after his NFL career and stayed there for 11 years.
O'Brien will return to the position he held prior to filling the Penn State head coaching vacancy in 2012.
Many Nittany Lions made their mark on the NFL's Divisional Round.