We describe a wide-field four-wave mixing (FWM) microscope with imaging characteristics optimized for examining nanostructures. The microscope employs surface-plasmon polariton (SPP) excitation in a gold film to achieve surface-sensitive imaging conditions. The SPP surface fields boost the FWM efficiency by 2 orders of magnitude relative to the excitation efficiency of the evanescent fields at a bare glass surface. We demonstrate two excitation geometries that completely suppress the electronic FWM response of the metal film while allowing the far-field detection of FWM radiation from nanostructures at the interface. We obtained wide-field FWM images from individual carbon nanotubes and nanoclusters of neocyanine molecules at image acquisition times of 1 s, demonstrating the potential for background free, surface-enhanced FWM imaging of nanomaterials.