The sum is half the record Lotto jackpot win - shared with a couple from Hawick who claimed their prize within days of the 9 January draw.
A spokesman for organisers Camelot urged players to "check, double-check and triple-check" their tickets.
The ticket had the winning numbers 26, 27, 46, 47, 52 and 58.
Updates on this story and more from Worcestershire
Camelot said the exact location where the ticket was purchased could not be revealed but it hoped that by naming the area where the ticket was bought it could increase local interest and help find the winner.
The area has not been narrowed down further to preserve the winner's anonymity, they said.
It is not known if the winning ticket was bought by an individual or a syndicate.
David and Carol Martin, both aged 54, received a cheque for £33,035,323 after claiming their share of the record jackpot, that occurred after 14 successive rollovers.
Even though the prize total was shared, the sum is still the biggest win since the National Lottery was launched in November 1994.
However, the sum is dwarfed by the the biggest UK win in the Euromillions lottery, a draw where prize money comes from ticket sales in several European countries.
Colin and Chris Weir, from Largs in North Ayrshire, collected £161.6m in 2011.

Matthew George was held by police investigating historical allegations at Kerelaw School.
The 67 year old taught art at the school and secure unit, which closed in 2006 following a police probe into incidents of abuse.
He is expected to appear at Kilmarnock Sheriff Court later.
A report is to be sent to the procurator fiscal.
The school was originally run by Strathclyde Regional Council and its successor, Glasgow City Council.

The Royal Institution of Chartered Surveyors (Rics) said the slowdown last month was fuelled in part by uncertainty over the EU referendum.
It also cited the higher stamp duty in place on investment property purchases.
New buyer inquiries fell significantly across Scotland, with 21% more surveyors reporting a fall in interest.
This was the sharpest decline since 2012.
There was also a further fall in the supply of properties coming on to the Scottish housing market, and a decline in sales for a second consecutive month.
Survey contributors said they expected that trend to continue, with 9% more respondents anticipating a further drop in sales over the next three months.
The same trend was projected across the UK, with 12% more contributors expecting transactions to fall over the next 12 months - the weakest reading in four years.
Rics chief economist Simon Rubinsohn said: "Big events such as elections typically do unsettle markets so it is no surprise that the EU referendum has been associated with a downturn in activity.
"However, even without the build-up to the vote and subsequent decision in favour of Brexit, it is likely that the housing numbers would have slowed during the second quarter of the year following the rush in many parts of the country from buy-to-let investors to secure purchases ahead of the tax changes.
"Rics data does suggest that the softer tone to the market will persist over the coming months but the critical influence looking further is how the economy performs in the wake of the uncertainty triggered by the vote to leave.
"Respondents to the survey are understandably cautious, but with interest rates heading lower and sterling significantly so, it remains to be seen whether the concerns about a possible stalling in both corporate investment and recruitment are justified."

Perry, 19, made his first team debut in the Football League Trophy in August before playing in the 1-0 win over Grimsby in the FA Cup in November.
The Liverpool-born midfielder came through the Wanderers' academy and was a regular in the club's Under-23 side.
However, Bolton, who were promoted from League One last season, have released full-back Callum Spooner.
An unclaimed National Lottery jackpot winning ticket that could earn the winner £33m was bought in the Worcester area, it has been revealed.
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A former teacher has been arrested in connection with sexual and physical abuse allegations at a former residential school in Ayrshire.
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House prices across Scotland have continued to rise despite a marked drop in housing market activity, according to a report.
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Young midfielder Alex Perry has signed a first professional contract with Championship side Bolton Wanderers.