The propagation of surface plasmon polaritons guided along Au metal waveguides fabricated by electron-beam lithography is experimentally investigated using simultaneous near-field excitation and detection of plasmon-polariton modes localized at the air/Au interface. The directly measured propagation characteristics of surface plasmon-polaritons agree well with simulation results obtained using full-vector calculations and the analytic dispersion of asymmetric plasmonic waveguides for thin Au films. Our results demonstrate that near-field excitation/detection schemes are well suited for direct imaging and characterization of propagating surface plasmon-fields bound to thin-film metal layers, and can be used for fast and reliable characterization of plasmonic waveguide elements and nanodevices.