Searches have been continuing in the Woodhall Spa area for Fred Gibson, just over a week after he went missing.
The 82-year-old was last seen in the village at about 1.45pm on Thursday, November 28.
Underwater search teams have been checking the River Witham, while officers have carried out house-to-house enquiries.
Speaking on Friday, Inspector Dave Penney said: “We are continuing to search for Fred, and it’s vital that anyone with information gets in contact with us – even the smallest detail may be crucial.
“The underwater searches are being carried out as a precaution, and we are in regular contact with Fred’s family during this very difficult time.
“If you have seen Fred or think you could help us to find him, then please get in touch.”
Fred is described as white, 5ft 10ins tall, with short hair. He was wearing a blue top, jeans and a sleeveless shooting jacket.
His car, an Audi Q5, was parked at 3.15pm on November 28 close to the Railway Inn at Kirkstead Bridge.
If you have information, call 101 quoting incident 384 of November 28.