Facebook Inc. (FB.O) said it plans to buy back US$9 billion more of its shares, in a bid to boost confidence in the company after a recent stock slump.

Facebook shares have fallen almost 40 per cent since the social-media giant said in July that it expects growth to slow and profit margins to narrow in coming years. Its main social network is reaching a saturation point, so it needs to explore new types of business models. The company has also been facing scandals over its handling of misinformation and user data.

Facebook said in a regulatory filing that its board had previously authorized share repurchases of up to US$15 billion as part of a program started in 2017. The US$9 billion buy back announced on Friday is in addition to those prior authorizations, the company said.

Facebook shares rose 1.4 per cent in extending trading. Earlier on Friday, the stock closed at US$137.42 in New York.