State leaders are looking for volunteers to help plant grass during an annual event at Delaware Seashore State Park and South Bethany.   Saturday's event is now in its 24rd year. Officials say planting the grass helps to build and stabilize sand dunes by trapping windblown sand. The dunes are essential to protecting Delaware's coastline during storms because without the dunes, storm waters can rush inland and damage property.  Last year approximately 800 people planted more than 150,000 stems of grass along four miles of shoreline.  Officials are asking volunteers to sign up by Wednesday either by e-mail or online. Volunteers will also be planting grass at Lewes Beach, but that site already has all the volunteers that are needed.