stephanie scott was last seen at leeton , 550 km west of sydney , on sunday .
high school teacher is due to marry her partner of five years on saturday .
police have grave concerns as her disappearance is ` out of character '
family fear her red mazda - also missing - may have rolled off the road .
they have asked the public to help search along roadsides in the area .
her parents plan to hire a private helicopter to assist with the search .
the 26-year-old spent the weekend she disappeared picking up cufflinks for the wedding and a bikini to take on her honeymoon to tahiti .
family have begun the heartbreaking task of cancelling wedding plans .