Airbnb's valuation is set to rise to $13 billion, up from $10 billion earlier this year, as it prepares an employee stock sale, according to people familiar with its plans.
The valuation would make the accommodation site second only to Uber in the rankings of Silicon Valley's most valuable private companies, at a time when some venture capitalists are becoming concerned about the rate at which start-ups are spending capital.
Airbnb, which overhauled the design of its site and apps this summer, is without a chief financial officer after the departure of Andrew Swain last month, which may make an initial public offering unlikely in the near term.
To allow employees to cash in on some of their stock in the meantime, Airbnb is talking to its existing investors about allowing them to buy back tens of millions of dollars worth of shares, according to two people familiar with the situation.
Read MoreSan Francisco moves closer to legalizing Airbnb
The funds would go to staff rather than raising new capital for the company, they said, and the terms are still being finalized. Airbnb declined to comment.
Momentum in private tech companies' valuations shows no sign of slowing despite recent gyrations on the public markets. Earlier this month, e-commerce company Square raised $150 million from investors at a valuation of $6 billion, which has doubled in two years.
Uber, whose offices are in the same building as Square in San Francisco, raised $1.2 billion in fresh capital at a $17 billion valuation this summer.
While few Silicon Valley investors will go as far as declaring that there is a another bubble in the tech world, some have begun to voice certain worries.
Read More Thiel: We are in a government bubble of massive size
Marc Andreessen, co-founder of Andreessen Horowitz, which is among Airbnb's investors, said in a series of tweets last month that he was worried by companies with high rates of cash burn.
"New founders in [the] last 10 years have ONLY been in [an] environment where money is always easy to raise at higher valuations. That will not last," he said. "When the market turns, and it will turn, we will find out who has been swimming without trunks on: many high burn rate co's will vaporize."
Airbnb, which was founded in chief executive Brian Chesky's bedroom in 2008, raised almost $500 million in April from TPG, T Rowe Price and Dragoneer Investment Group, taking its total raised to around $800 million.
Like Uber, Airbnb continues to face regulatory challenges around the world. Earlier this month, New York attorney-general Eric Schneiderman said that nearly three quarters of Airbnb rentals there were illegal, in what is the company's largest market.
More from the Financial Times:
EU tells Britain to pay extra €2.1bn
Tesco admits overstating profits for longer
Amazon shares tumble as losses blow out
By contrast, in its home town of San Francisco, Airbnb will soon become more legitimate – and more regulated – with a new law allowing short-term rentals by homeowners. However, the law is proving controversial, with California state senator Dianne Feinstein calling the action "shortsighted" for driving home rental costs higher and threatening a "blanket commercialization of our neighborhoods".
Airbnb's funding talks were earlier reported by the Wall Street Journal.