A team of officers using specialist PSNI search dogs are conducting searches at a number of locations in Co Tyrone, police said today.
The Castlederg teenager went missing after a night out in Bundoran in 1994.
Chief suspect and convicted child killer, Robert Howard, who was acquitted of Arlene’s murder in 2005, was seen with her before she died.
The jury in the case wasn’t told of his previous convictions.
A PSNI spokesman said the resumed operation had the “twin objectives of recovering the schoolgirl’s remains and progressing the investigation”.
“The sites to be covered in this phase of the search strategy have links to the overall investigation into Arlene’s disappearance and murder,” police said in a statement.
“Searches will continue to be conducted on a planned roll-out, depending on weather conditions, availability of resources and operational commitments.”
Detectives from the serious crime branch have been in contact with Arlene’s family to keep them updated.