Reality TV star Kylie Jenner wiped $1.3bn (£1bn) off Snap’s stock market value after tweeting that she no longer used its Snapchat messaging app.
Celebrity Kim Kardashian’s half-sister posted: “sooo does anyone else not open Snapchat anymore? Or is it just me… ugh this is so sad.”
Snap’s shares sank after Ms Jenner’s tweet about Snapchat’s re-design to her 24.5 million Twitter followers.
One million people signed a petition demanding Snap roll back the change.
After dropping almost 8%, shares in Snap closed 6% down on Wall Street, and are now back near the $17 price at which the shares were listed when the company floated on the stock market in March of last year.
Snapchat is facing intense competition from Facebook’s Instagram – especially for celebrity users – and Ms Jenner’s attack comes at a time when investors are already worried.
Ms Jenner later tweeted a follow-up: “still love you tho snap… my first love”.
Snap has rejected complaints about November’s re-design to its messaging app, with its boss Evan Spiegel saying earlier this month that users just needed time to get used to it.
Mr Spiegel had something to soften the blow, though, with news on Thursday that his total pay last year was a staggering $637.8m.
It is thought to be the third-highest annual package ever received by a company’s chief executive.
The remuneration was, however, heavily boosted by the award of shares when the company listed on the stock market.
Snapchat’s shares have been particularly volatile since the company went public last year, with investor profits sometimes evaporating as fast as pictures and messages disappear from the site.
The shares plunged by 17% in August, after disappointing results.
But in the first weeks of this month shares bounced back by almost 50% after Snapchat reported a 72% rise in sales in the last quarter of 2017, with no fewer than 187 million people using the site every day.
“Part of the problem is Snap isn’t profitable at the moment, so there’s a fair amount of hope for the future already baked into the share price, making it particularly vulnerable to swings in sentiment,” said Laith Khalaf, senior analyst at Hargreaves Lansdown.
“Snap’s future rests on building user numbers, so anything which could undermine that journey is naturally going to unsettle investors.”