Rishi Sunak’s campaign has poured almost £24,000 into Facebook advertising since the middle of July, heavily outspending his Tory leadership rival Liz Truss.
The former chancellor has spent £23,810 on 208 adverts since July 16, according to data from Facebook’s advert library.
The money has been used to promote posts from both Mr Sunak’s personal Facebook page and one for his campaign named Ready4Rishi, and has made him one of the top 20 UK spenders on Facebook advertising in the past month.
Ms Truss has spent far less, paying £6,590 to promote 20 adverts over the same period.
On August 14, the most recent day for which data is available, Ms Truss’s campaign recorded no spending on Facebook advertising while Mr Sunak’s campaign spent £1,635.
A spokesperson for Mr Sunak’s campaign said: “There all kinds of ways to communicate Rishi’s message and online advertising is an effective one that has the potential to reach millions of people every week.
“It’s vital people understand what Rishi has to offer the country, particularly in what is going to be challenging times for the country.”
In line with what is understood to be the age profile of Conservative members, data from Facebook shows both candidates have mainly targeted their adverts at older users.
Several of Ms Truss’s adverts, for example, were not shown to anyone under the age of 35 while those aged over 65 made up the bulk of recipients.
Mr Sunak’s adverts are understood to be targeted at members and to have encouraged 10,000 of them to sign up to his campaign.
The Labour Party has also used the Tory leadership contest as a spur for Facebook advertising, using some of the £10,200 it has spent since July 16 to promote posts critical of the candidates.
In recent days, these have mainly focused on the frontrunner, Ms Truss, but the party’s single largest spend on an attack ad involved Mr Sunak.
On August 10, Labour spent between £2,000 and £2,500 promoting a post featuring a video in which the former chancellor boasted to an audience in Tunbridge Wells that he had diverted funds from “deprived urban areas” to more prosperous towns.
Labour described his comments as “scandalous” but Mr Sunak defended them by saying he was “making the point that deprivation exists right across our country”.
The advert featuring the video was seen by between 600,000 and 700,000 people, according to Facebook data.
In contrast, the Conservative Party’s official Facebook page has had just one advertising campaign in the past month, promoting a post encouraging users to tell the next prime minister what their priorities are.
The advert cost £997 and was overwhelmingly targeted at older Facebook users, with 72% of those shown the post aged over 65 and another 12% aged between 55 and 64.