The 55-year-old was last seen in Eastbourne town centre on Saturday, April 8.
He is described as a stocky white man, 6’1″, with grey hair.
Gareth is believed to be wearing a white puffa-style coat, a white hooded jumper underneath, and dark jogging bottoms.
Anyone who sees him or knows his whereabouts is asked to call 999 and quoting serial 1151 of 08/04.