This is the ninth bird to disappear in suspicious circumstances in the last 12 weeks.
The bird, named Arthur, hatched from a nest in the Peak District this summer.
This was the first time hen harriers had successfully bred in the Peak District since 2015.
Arthur, along with his sister Octavia, was fitted with a lightweight satellite tag by RSPB staff as part of the Hen Harrier LIFE project, which has enabled the RSPB to track his movements since leaving the nest in July.
Scarborough officially smashes temperature record as Met Office confirms new hottest day
Post-war asbestos bungalows to be demolished in Scarborough as plans for new terraced homes approved
RNLI issue weever fish warning for Yorkshire coast
Whitby Regatta - here's what's going on at this year's event
Firefighters respond to arson attacks in Scarborough and fires near Malton and Whitby
On the morning of Friday October 26, he flew onto the North York Moors National Park, having previously been in Nidderdale.
He registered his last position at 9.55am when he was just north of Lowna Bridge, near Hutton-le-Hole.
RSPB Investigations staff searched the area of the bird’s last known location but found no sign of either a tag or a body – prompting concerns that the bird may have been deliberately killed and the tag destroyed.
In August, his sister Octavia’s tag also suddenly cut out, with her last location coming from a driven grouse moor in the Peak District. No trace was found of her either. The police and the RSPB are appealing for information.
RSPB Assistant Investigations Officer Jack Ashton-Booth said: “Arthur’s last location showed he was in an upland area close to several driven grouse moors.
“When tagged, hen harriers have died of natural causes in the past, the tags and bodies of the bird are usually recovered.
“To find no trace of Arthur or Octavia is extremely concerning. Arthur is the ninth hen harrier to suddenly disappear in suspicious circumstances since August.
“This is gravely concerning given that the species is on the brink of extinction as a breeding bird in England.”