Police have issued this new picture of Denise Gray as officers continue to search for her in the Revesby area this afternoon.
She has not been seen since she left a property where she was staying in Revesby at lunchtime on Monday to go for a walk.
The News can reveal there have been two further unconfirmed reports that Mrs Gray was seen in Revesby village at around 5pm.
She was reported missing at 5.45pm.
Police have called in specialist teams who have been searching a large area, including Revesby Estate.
Apart from officers on foot, the operation has involved a helicopter, dog teams, the fire service and officers who are experts in searching water.
The search is being co-ordinated at Horncastle Police Station by Chief Inspector Mark French.
He said: “Denise has been missing for 48 hours and we are becoming increasingly concerned about her safety.
“The immediate search was focussed on Revesby, but there is a chance that she could have reached other villages.
“We’d ask people in places like East Kirkby, Mareham le Fen and Revesby to look in outbuildings - and any additional land they might be aware of.
“We are aware the last two nights have been very cold and it could be that Denise has wandered into an outbuilding to keep warm.
“We have all our available resources searching but obviously it is a big rural area and there is only so much we can do.”
Chief Inspector French confirmed Mrs Gray was in England on a visitor visa and was saying with a friend in Revesby.
He added: “Our understanding is she has been here a while and knew some of the area although she does not have extensive knowledge.
“She hasn’t got an extensive group of friends so that is a line of enquiry we can’t go down.
“We are in the process of following up the two later sightings on Monday at around 5pm but at this stage, there is no further information from them.”
Chief Inspector French said he was constantly monitoring the situation and revealed additional officers could be brought in.
Officers are checking water courses in the area - including dykes - and lakes in the Revesby Estate. They are also searching extensive areas of woodland.
Chief Inspector French added: “At this stage, we are not asking for volunteers but if people could check their outbuildings it would be a big help.”
Police have not ruled out the possibility that Mrs Gray might have left the Revesby area, either on foot or in a vehicle.
Police have checked with local bus and taxi companies, without success.
Chief Inspector French confirmed Mrs Gray was on medication, but officers are not certain whether she had the medication with her when she set out for a walk.
Mrs Gray is a US citizen with a strong American accent. She is 5’8” tall, of slim build, Hispanic appearance and has dark, shoulder-length curly hair.
She was wearing a short maroon/red jacket and black trousers and also wears glasses.
Anyone who has seen someone matching her description, or who has any information which might assist the enquiry, should contact 101, quoting the incident number 346 of 3 March 2014