We report the first observation of nonequilibrium heating of the electronic and lattice modes in a thin silver film enhanced due to the excitation of single metal-boundary surface plasmons at a metal-air interface. The heating enhancement due to plasmon decay is more than two orders of magnitude as compared to heating by a directly incident laser beam. The heating is probed on a picosecond time-scale by thermally-induced changes in the ultraviolet reflectivity of the film.