Many vibration-based structural damage detection techniques which perform damage diagnosis of a structure based on structural dynamic characteristic parameters have been proposed in the last two decades. One of the promising approaches proposed recently is the local flexibility method. The local flexibility method, which is founded on virtual forces that cause nonzero stresses in a local part of the structure, can estimate damage locations and local stiffness variations of beam structures. It does not require a finite element model of the beam structure. The structural modal parameters identified from the ambient vibration signals both before and after damage are the key information for the local flexibility method. The number of modes necessary for the local flexibility method is usually quite small, especially for a simply supported beam where only the first mode could be sufficient. However, for a hyperstatic beam, the number of modes required for estimation of the damage could be much higher. This makes the feasibility of the local flexibility method much lower because in practice only the first few modes could be identified with high quality using ambient vibration signals. Therefore, in this study, non-local virtual forces which cause concentrated stresses in a local part and nonzero stresses in the other parts of a structure are employed. The theoretical basis of the proposed method which uses non-local virtual forces is derived. The proposed method is validated with a continuous steel beam experiment. The results illustrate that the non-local virtual forces can determine the local variations of stiffness more accurately with less identified modes. Therefore, the feasibility of the proposed method is higher because limited number of high quality modes can be iden