The electric conductivity of atomically thick materials such as graphene yields an effective complex permittivity with a negative real part in the infrared spectrum. This feature allows for the propagation of slowly decaying electromagnetic waves, called surface plasmons-polaritons (SPPs), that are confined near the material interface with wavelengths much shorter than the wavelength of the free-space radiation. In this talk a finite element approach for the simulation of SPP structures on a conducting sheet is presented. Numerical results for singular geometries, e.g., sheets with sharp edges, and finite resonating strips are discussed.