Twisting vibrations of coaxial-composite-nanowires with damages and imperfect interface are of great concern. For this purpose, the nonlocal-surface energy-based equations of motion are carefully derived for bimaterially defected nanowires using differential- and integral-based nonlocal models (DNM & INM). For the differential-based modeling, the admissible mode shapes of the damaged nanostructure are appropriately extracted accounting for nonlocality and surface energy effect, and the twisting frequencies are evaluated for various end conditions. For all proposed models, reproducing kernel particle method (RKPM) is also adopted, and the problem is solved for general boundary conditions by employing Hamilton’s principle. The predicted results by the meshless approach based on the DNM are successfully compared with those of the Galerkin-based admissible mode method. Through verifying the INM’s results and the DNM’s results, a comprehensive parametric study is performed to examine the roles of the location and intensity of damages, nonlocality, surface energy, imperfect interface parameter, and geometry of the nanostructure on its twisting behavior.