Twitter Inc. expects to generate at least $1 billion in sales in 2014, two people with knowledge of the matter said, indicating that the microblogging service will grow about twice as fast as some analysts now predict, Bloomberg reported.

Twitter based the forecasts on expected advertising demand, said the people, who asked not to be identified because the numbers are private. The San Francisco-based company could change or miss the forecasts, the people said.

Demand for advertising aimed at Twitter's more than 140 million users is benefiting the company. Researchers at EMarketer Inc. have said that in 2014, Twitter will reach $540 million in ad sales, which make up virtually all of its revenue, up from $139.5 million last year.

Even so, it will take Twitter longer to generate $1 billion than bigger competitors Facebook Inc. and Google Inc.

"The marketers who have used Twitter's advertising opportunities have been pleased," said Nate Elliott, an analyst with Forrester Research Inc. "Twitter's going to be able to push forward and continue to make more money from it."

Google crossed the $1 billion threshold five years after its founding, while Facebook, which sold shares in an initial public offering last month, achieved that goal six years after it got started. Founded in 2006, Twitter will be 8 years old in 2014.