This paper describes the application of an active structural health monitoring technique for a composite plate bonded with a distributed piezoceramic patches array. An optimal placement of these patches has been proposed using grammians of controllability and observability and the H∞ modal norm. The proposed approach was established via finite element modelization (FE) of the composite structure. With this optimal placement, an active structural health monitoring scheme has been accomplished. Therefore, using spatial information given by the distributed sensors, we propose two damage indices (DI). These indices are able to detect and localize damages. The first DI is based upon non-parametric frequency response function estimates; the damage is detectable when changes in the estimates exceed their normal statistical bounds. The second DI uses change in the energy signal sensor to localize damage existing in the composite structure. The efficiency of the proposed approach is demonstrated through experimental tests.