A top cop says he is “extremely concerned” for a missing 76-year-old woman as police appealed again for help finding her.

It has now been a week since Iona, whose last name has not been revealed, was last seen near Witney town centre on Monday at around 11am.

Thames Valley Police has been searching the River Windrush, using helicopters, drones and divers, but are still stumped as to her whereabouts.

READ MORE: 'These youngsters saw robbery,' police say

Oxford Mail: Missing Iona was last seen a week agoMissing Iona was last seen a week agoMissing Iona was last seen a week agoMissing Iona was last seen a week ago (Image: TVP)

In an anniversary appeal today (Monday), Chief Inspector James Sullivan said: “We’re extremely concerned for the welfare of Iona, who was reported missing around a week ago.

“As part of our enquiries, searches continue to be conducted at the River Windrush in Witney. However we are keeping an open mind and following all lines of enquiry.

"I am appealing to anybody who believes that they might have seen her, or who has any information that may help us to locate her to please get in touch with Thames Valley Police.”

Iona is approximately 5ft 6ins tall, of slim build, and was last seen wearing a brown three-quarter length coat with fur around the hood, leggings and black Nike trainers.

Oxford Mail: The search continues for IonaThe search continues for Iona (Image: Sarah Dalton)

The Avon & Somerset specialist dive team have conducted a detailed underwater search of at least two kilometres of the river with no luck.

People can report sightings or information via the force’s dedicated missing person portal. 

They can also call 999, quoting the reference 43240068765.