We introduce a secular semiempirical model of the Pariser-Parr-Pople type to reproduce the electronic structure and polarizability of the C-60 fullerene. The model is then used to simulate the response of this molecule to an electric charge and estimate its polarization energy. By expressing the charge potential at the C-60-cage surface as a multipole expansion, an analytical form is obtained for the polarization energy. Application of these results to endo- and exohedral complexes of alkali ions gives data in rather good agreement with recent ab initio calculations [Hira and Ray, Phys. Rev. A 52, 141 (1995)].