Identification of modal parameters from output-only data is studied in this work. The proposed methodology uses transmissibility functions obtained under different loading conditions to identify resonances and mode shapes. The technique is demonstrated with numerical simulations on a 2-DOF system and a cantilever beam. To underpin the simulations, a real test was done on a beam to show the efficiency of the method. A practical application of the method can be to identify structures subjected to moving loads. This is demonstrated by using FEM-model of a cantilever beam with a moving load.