LONDON, March 20 (Reuters) - Manchester United are trailing Manchester City this season on the pitch but are peerless when it comes to their social media muscle, according to a report published this week.

The Old Trafford giants, who topped Deloitte's Money League in January for the world's richest clubs, also came out top of the Social Network Rankings for the Premier League in 2017.

The report, produced by Newton Insight, ranked England's 20 top-flight according to eight performance indicators across various social media platforms.

United beat Manchester City to first place with Chelsea third, Arsenal fourth, Liverpool fifth and Tottenham Hotspur in seventh place. Huddersfield Town were a surprising sixth with Stoke City bottom of the pile.

United had 73.7 million Facebook followers in 2017, 16.5 million Twitter fans and 20 million Instagram followers.

City had 29 million, 5.5 million and 5.9 million respectively for the same categories.

United also had most followers of the 20 Premier League clubs on Chinese social media platform Weibo -- 9.2 million.

Fans of the Red Devils made up 30 percent of all Premier League followers and the club accounted for 40 percent of all Premier League fan engagement on social media in 2017.

"The best way to describe Manchester United's approach to building its global fanbase is 'relentless'," the report said.

"The club is not sitting back defending its lead, it keeps pressing forward. They have more resources than most to support its ambitions but the club is also committed to producing creative content and driving fan engagement."

The Social Network Rankings were calculated using indicators such as fan engagement, growth, total number of club posts and the amount of days it takes clubs to add 10,000 new followers on a given platform.

While newly-promoted Huddersfield's 113,000 Facebook followers was dwarfed by the bigger clubs it represented an 80 percent rise in a year while their Instagram figures rose by 600 percent -- proof of the appeal of the Premier League.

Huddersfield made huge efforts to increase the club's profile on the back of promotion, racking up 18,000 social media posts in 2017, behind only Chelsea, United and City.

"Smaller teams may struggle to compete financially with the top teams, but Huddersfield's digital performance should encourage other clubs looking to increase brand exposure," the report said.

While the combined 250 million Facebook followers of the Premier League made it the most used format for fans, that figure represented only a five percent yearly rise compared to the 49 and 33 percent increases enjoyed by Twitter and Instagram.

"Facebook appears to have reached maturity," the report said. "Twitter's immediacy lends itself to the drama of live football. It feeds the endless appetite for gossip."

China is regarded as a huge, and relatively untapped market, although still something of a puzzle, according to the report.

Arsenal and Liverpool were the first to set up social media sites on Weibo in 2011, since when Premier League clubs have amassed a combined fanbase of 30 million followers. (Reporting by Martyn Herman Editing by Toby Davis)