Without Donald Trump, Twitter could lose almost a fifth of its value.

That's the conclusion of Monness Crespi Hardt & Co. analyst James Cakmak, who said that the social media company would see as much as $US2 billion ($2.5 billion) in market value wiped out if @realDonaldTrump quit tweeting.

Don't thank me: President Donald Trump is a prolific user of Twitter. Credit:AP

It's not that the president's defection would touch off a mass exodus, lowering the number of "monetisable" daily active users, Cakmak said in an interview. Instead, losing its most prominent user would hit Twitter's intangible value and lead to what's known as multiple compression.

"There is no better free advertising in the world than the president of the United States," said Cakmak, who has a neutral rating on Twitter shares.