Celebrity endorsements can make a company a lot of money, but a celebrity or influencer that turns her back on a product can have devastating results.
Kim Kardashian’s younger sister Kylie Jenner wiped $1.3bn (€1.06bn) off Snap's stock market value after tweeting that she no longer used its Snapchat messaging app.
Snap's shares sank after Ms Jenner's tweet about Snapchat's re-design to her 24.5 million Twitter followers.
Ms Jenner later tweeted a follow-up.
After dropping almost eight per cent, shares in Snap closed six per cent 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 Instagram, which is owned by Facebook, and Ms Jenner's attack comes at a time when investors are already concerned.
Snap has rejected complaints about its re-design. Founder Evan Spiegel said earlier this month that users just needed time to get used to it.
Mr Spiegel’s total pay last year was $637.8 million, the third-highest annual package ever received by a company's CEO.