The father of a missing American hillwalker who was last seen in Donegal is due to join the search tomorrow.
Kelly Jones (41), from Texas, works in the catering industry in Charleston, South Carolina, and was travelling around Ireland alone.
Her father Ricky will fly in from Georgia in the hope of finding his daughter.
He told gardai that he was praying she may have moved location from the Donegal hostel she was staying in, without telling anyone.
Hundreds of volunteers yesterday combed more than 50 square kilometres of countryside in a desperate search for Kelly.
She vanished on Saturday not long after leaving a hostel near Glencolmcille, Co Donegal.
Coastguard, mountain rescue and hillwalking club volunteers spent a fourth day searching for Ms Jones.
The searches on land and sea -- supported by the Sligo coastguard helicopter -- were concentrated around Sliabh League, Europe's highest seacliffs, three times higher than the Cliffs of Moher.
Donegal Mountain Rescue co-ordinator Brian Murray said: "Kelly's father has told us that she had told him she wanted to see the cliffs at Sliabh League before leaving Donegal, so we concentrated our searches there.
"Unfortunately our search has failed to yield any clue as to what happened to her."
Gardai say they are investigating "all possibilities" in their investigation.