Arlene Arkinson, 15, from Castlederg in Co Tyrone disappeared in August 1994 after a night out across the Irish border in Co Donegal.
She was last seen being driven off down a country road late at night by child killer Robert Howard.
He was acquitted of the schoolgirl’s murder in 2005 by a jury not told about his lengthy criminal history which included killing another teenager, Hannah Williams, in south London several years earlier.
Arlene’s body has never been found despite extensive searches.
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Howard remained the prime suspect in the unsolved case until his death in an English prison last year.
The new searches are focused on farmland at Killen, around a mile from Castlederg, close to where Arlene was last seen. The operation was triggered after a report of some disturbed earth.
Police Service of Northern Ireland (PSNI) Detective Chief Superintendent Raymond Murray said: “The family of Arlene Arkinson have been advised of this development purely as a precautionary measure.
“It would be premature to draw any inference from this initial report or the police response to it at this time.”