The paper extends the classical problem of nonlinear panel flutter to the analysis of the effects of external forcing on aerodynamically self-excited thin plates structures of high speed vehicles. This phenomenon can be induced by the aeroeacoustic excitation of noise, boundary layer, or oscillating shock waves. The problem is formulated within nonlinear elastic and linear aerodynamic theories by using a complex finite element model consisting of fifth order plate and second order membrane triangular elements. The excitation is applied harmonically as uniformly distributed pressures. In most cases the pattern of the dynamic response includes a transient period in which the fluttering motion is disturbed into a forced vibration (the steady-state motion) having the same frequency as the excitation. There are also conditions for complex motions having larger amplitudes (than those of the free auto-oscillating system) of both frequencies of flutter and excitation, respectively.