As huge numbers of bargain-hunters prepare to log on for the so-called Black Friday tomorrow, officers highlighted the growing trend for criminals to use social media to target potential victims with apparently attractive deals.
Figures show that last year victims reported losing more than £10 million to fraudsters when shopping online for Christmas presents.
One victim lost £86,000 when they tried to purchase a boat from a fraudster on eBay, police said.
Some 12,142 people said they had been bitten by online shopping fraud during the last Christmas period - with 133 saying they had been defrauded on Black Friday and another 115 falling victim on “Cyber Monday”.
City of London Police, who run the national reporting centre Action Fraud, is launching an awareness campaign aimed at helping shoppers avoid being conned.
Commander Chris Greany, the National Co-ordinator for Economic Crime, said: “Christmas is prime time for fraudsters to take advantage of the British public.
“During the festive season people rush to buy the presents they have been asking for; however, fraudsters see this period of generosity as an opportunity to strike and steal money from unsuspecting victims.
“Our campaign is designed to give individuals up-to-date advice that will keep them one step ahead of the criminals that target UK shoppers from all over the globe.
“Everyone deserves a crime-free Christmas so make sure it’s the criminals that are left short-changed this festive period.”
Young people are increasingly being approached on social media channels by fraudsters who offer seemingly great Christmas shopping deals, according to the police force.
It said that last year more people than ever reported that they had been initially approached on Instagram, with a 67% increase compared with the year before.
Analysis of Action Fraud reports from last Christmas showed that Items such as home electricals, mobile phones and jewellery were the most common items which fraudsters offered to victims.
Separate research published earlier this week found that nearly a third of online shoppers may be tempted to put themselves at risk of fraud during the frenzy to grab a Christmas bargain.
Criminals use scam emails, fake ads on social media or internet searches promising heavy discounts for desirable goods to trick people into visiting fake websites and entering their card details.
Once fraudsters harvest this information, they use victims’ details to go on shopping sprees.