You should be able to perform the following AddressToLocationAsync call.
public MainPage()
{
InitializeComponent();
Locator l = new Locator("Your GeocodeServer URL - v10 & up");
AddressToLocationsParameters p = new AddressToLocationsParameters()
{
OutSpatialReference = new SpatialReference(4326)
};
p.Address["Street"] = "380 New York St.";
p.Address["City"] = "Redlands";
p.Address["State"] = "CA";
p.Address["ZIP"] = "92373";
p.OutFields.Add("*");
l.AddressToLocationsCompleted += l_AddressToLocationsCompleted;
l.AddressToLocationsAsync(p);
}
void l_AddressToLocationsCompleted(object sender, AddressToLocationsEventArgs e)
{
}