Moss and other types of weedy plants usually move into a lawn when the lawn grass is no longer able to compete successfully for space or is in such poor condtion that weeds move in and take over. So you need to find out what is not allowing the grass to grow successfull and correct that. Things like compacted soils, shade, poor drainage etc favor moss and not grass. so if you go in and aerate, fertilize, improve the growing conditions for grass it may out compete the moss. Jus tusing weed and feed will probably not be the solution by itself.