A particle tracing method integrated into an unsteady Navier-Stokes solver with structured 2-D grids is presented. Particles may be released anywhere in the flowfield and are traced in time by convecting them with the local flow velocity. The localization of the particles is based on a sequential and directional search algorithm. The search algorithm provides interpolation weights at the localization point, which is needed to evaluate the local flow velocity. The method is applied to unsteady flow-fields over an impulsively started airfoil at an incidence, a single flapping airfoil, and a stationary airfoil/oscillating flap combination in tandem. It is shown that the method is accurate, efficient and robust, and remarkably captures the unsteady nature of the flowfields.