In this paper, the energy interpretation of the asymptotic Krylov-Bogoljubov-Mitropljski method was used to compile the first approximation of the solution and system of differential equations of the first approximation for the amplitude and phase of the single-frequency regime of forced transverse oscillations of continuous beams. General patterns are given for the arbitrary case of linear boundary conditions of a continuous beam, if the system of eigenfunctions and eigencircular frequencies of the undisturbed form of oscillation of the continuous beam is known. An expression is given for the mean value of the virtual work of the disruptive coercive force acting on the beam. The instantaneous circular frequency of the external force is a slowly-varying function of time. The derived equations are used to analyze linear and nonlinear forced transverse single-frequency oscillations of continuous beams for the case of stationary and non-stationary resonant conditions. Amplitude-frequency graphs are given for the case of stationary and non-stationary resonant conditions, and in the conditions of increasing and decreasing frequency of external noise.