The problems of optimum distribution of stiffener-actuators manufactured from piezoelectric or shape memory alloy materials and bonded to or embedded within the facings of a sandwich plate are considered. The sandwich plate consists of thin composite or isotropic facings and a thick shear deformable core. The amplitude of forced vibrations of the plate is reduced using symmetric couples of piezoelectric actuators subjected to out-of-phase dynamic voltages. Shape memory alloy stiffener-actuators are used to reduce bending deformations. In the latter case, a desirable effect is achieved by activating the stiffeners on one side of the middle surface. Optimum design is considered based on the requirement of minimal transverse static or dynamic deflections subject to a constraint on the volume of the material of the actuators. The variables employed in the process of optimization are the ratios of the cross sectional areas of the stiffener-actuators in each direction to their respective spacings. It is shown, that, dependent on the load, materials, and geometry, optimization can significantly reduce deflections, i.e. enhance the strength, of sandwich plates.