Anthony Smith, 38, failed to return to HMP Kirkham on Saturday, August 11 and has not been seen since, say police.
Smith, who was serving a sentence for drug offences, is known to have links to the Merseyside, Lytham and St Annes area.
He is described as five ft 10ins tall with blue eyes and blond hair. He has a scar on his right eyebrow and a tattoo of ‘Tyson’ on his right arm and boxing gloves on his left.
Anyone who sees him or knows where he may be should call police on 101 quoting log number 1457 of August 11.