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The dispersion relation and propagation of surface plasmons polaritons (SPPs) on nanoporous gold films is experimentally investigated and an increasing red shift of the SPPs is observed with rising porosity. This is caused by a less negative effective dielectric constant of the nanoporous metal films and is predicted by classical Bruggeman or specific two dimensional Maxwell-Garnett effective medium models. The dispersion relation data is supported with leakage radiation microscopy enabling the determination of the propagation length and losses of surface plasmons on these nanoporous films. These results demonstrate how the control of the nanoporosity of metal layers leads to designer plasmons in the visible and near infrared allowing the tuning of the SPP dispersion to match the requirements of certain applications.