Source: United Kingdom Thames Valley Police
James Delahoyde, aged 40, was last seen at the prison at 8.15pm on Friday 21 April 2017.
Delahoyde is white, slim, about 6ft, with receding dark brown hair and brown eyes.
Delahoyde is a prisoner at HMP Springhill following a conviction for drugs offences.
Investigating officer, Detective Sergeant Andy Jones of the Investigation Hub based at Aylesbury police station, said: “We are re-appealing for any information as to the whereabouts of James Delahoyde.
“Despite a thorough investigation and two public appeals there have been no sightings of Delahoyde, who has links to Maidenhead and Slough, since he went missing.
“If you see Delahoyde or know where he is please call 999, or call 101 with any other information quoting reference 65 (22/4/17).
“We would ask that you do not approach Delahoyde, instead contact police as soon as possible.
“If you don’t want to speak to police directly you can always call Crimestoppers anonymously on 0800 555 111.”