A massive £6.3 million Lotto jackpot prize has gone unclaimed for more than two weeks, organiser Camelot said.
The lucky millionaire-to-be purchased their ticket in Anglesey or Gwynedd, North Wales, and matched the six winning numbers of 8, 15, 21, 26, 28, 32 which were drawn on Saturday, September 8.
A National Lottery spokesman said: "We're desperate to find this mystery ticket-holder and unite them with their winnings - this amazing prize could really make a huge difference to somebody's life.
"We're urging everyone to check their old tickets again or look anywhere a missing ticket could be hiding.
"Try checking in the pockets of clothing, in wallets, bags and down the back of the sofa - someone out there could literally be sitting on a fortune.
"We have the champagne on ice and our fingers crossed that the lucky winner comes forward to claim their win."
The winning ticket-holder has until Thursday, March 7 2013 to claim their prize and if no one comes forward then the money, plus all the interest it has generated, will go to the National Lottery Good Causes.
The map was commissioned to mark Tuesday night's EuroMillions roll-over which is now a staggering £138 million - the fifth biggest jackpot ever offered in the UK.</p>
Should anyone scoop the jackpot, their wealth will be slightly less than Europe's biggest Lottery winners Colin and Chris Weir, from Largs in Ayrshire. The husband and wife made the headlines in July when they won £161,653,000, thanks to several rollovers.</p>
Boasting 164 National Lottery millionaires, one in 14,211 North East residents has now banked a seven-figure jackpot prize. Winners Paul and Christine Goldie from Washington, near Sunderland, pocketed £3,581,481 after their numbers came up on Christmas Day last year.</p>
The Millionaire Map, which includes both publicity and non-publicity winners, is based on the number of millionaires created per adult population. One man who did go public with his winnings was Wayne Hughes from Holyhead on Anglesey, north Wales. The shop worker scooped £1,117,779 last August and even had the winning numbers tattooed on his arm.</p>
The region with the fewest millionaire jackpot winners was Northern Ireland, where only 53 seven-figure or more winners were created.</p>
Wales has seen 179 millionaires - one person in 14,502 - created over the last 16 years. Rugby fans Terry Roberts, Mike Williams, Lance Gifford and Gerwyn Jones, from the Rhondda Valley in south Wales, split £4,091,609 in April this year.</p>