A vibration based damage identification method is investigated experimentally. The dynamic response of an intact and a locally damaged 16-layer unidirectional carbon fibre PEKK reinforced plate structure with two stiffener sections is considered. A forced-vibration set-up, including a laser vibrometer system, is employed to measure the dynamic behaviour. The feasibility of the two-dimensional Modal Strain Energy Damage Index algorithm to detect and localize impact induced defects is demonstrated.