Dynamic experimental studies on horizontal interaction factors for laterally loaded model soil-pile systems subjected to low-to-high amplitude pile head loading are reported, focusing on the effect of dynamics and local non-linearity. Results obtained from dynamic experiments with different amplitudes of harmonic lateral loading on instrumented model soil-pile systems conducted on a shaking table indicate that the resonance of soil-pile system shows a profound impact on the horizontal interaction factors. Furthermore, behavior of the soil-pile system becomes highly non-linear with increasing amplitude of loading, as the extent of local non-linearity around the pile increases. Consequently, group effects cannot be predicted by using established approximate equations based on the assumption of linear viscoelastic behavior. To this end, new semi-empirical equations are proposed for obtaining the horizontal interaction factors, as an extension of available approximate equations to incorporate the local non-linear behavior of soil-pile system for both small and large pile spacings.