Underwater search and rescue teams have trawled the River Wyre at Scorton close the spot where David Thomson's car was found abandoned.
The 26-year-old, from Poulton, who was left with brain damage following a serious car crash, has not been seen since January 16.
Underwater police search teams have now extended the hunt for Mr Thomson to the river close to the Six Arches caravan park in Scorton.
Mr Thomson's blue Vauxhall Astra van was discovered nearby the day after he disappeared.
His friends, who have set up the group Please Find David Thomson on social networking website Facebook, have carried out searches of fields in the same area.
Mr Thomson's mother, Maggie Hanson, 57, said: "I just can't imagine where he is."
Mr Thomson is described as 5ft 8ins tall, white, with short brown hair and blue eyes. He could be wearing a black hooded top, dark blue jeans and black Rockport boots.
Anyone with any information should contact Fleetwood Police on (01253) 876611 or (01253) 604378 or Crimestoppers 0800 555 111.