Photonic topological insulators (PTIs) are electromagnetic structures with highly robust uni-directional edge states, originating from their non-trivial bulk band topology. Here, we propose a plasmonic PTI that supports highly confined one-way edge states capable of transporting deep subwavelength optical frequency plasmons through arbitrary paths without back-scattering. The structure consists of a simple planar array of coupled plasmonic nanoparticles arranged in a perturbed honeycomb lattice, that exhibits non-trivial band topology. The operation frequency of the emergent edge states is shown to be independent of the lattice constant allowing for the miniaturization of the structure. As a high frequency PTI with a simple and planar design, this structure is compatible with well-established integrated nanofabrication technologies and may find application in planar, compact and topologically robust integrated nanophotonic devices.