The first thing to check is the condition of the tyres, the characteristics can change as they wear, check for eveness of wear across the tyre, you could try swapping them round. Tracking error won't in itself cause the car to pull to one side but it will cause uneven tyre wear. If the tyres are in order its most likely an alignment problem but not tow in, rather camber ar castor angle which are not normally adjustable but can be upset by damage.