Isovector methods are a recently developed technique for systematically investigating properties of the solutions of systems of differential equations. These methods are applied to the nonlinear equations of power law creep with elastic strains under conditions of plane and antiplane strain. Among the results are a family of self-similar solutions which are shown to be the only ones extant for the cases investigated. Some light is also shed upon the existence of conservation laws for these equations, and upon the existence of mappings which transform the governing equations into a set of equivalent linear equations.