Telegram's founder Pavel Durov said Tuesday that the encrypted messenger app had added a "record" 70 million users in one day after Facebook was hit by a massive outage.
Potentially billions of users were impacted Monday when the dominant social network and its Instagram and WhatsApp platforms went offline for seven hours.
Telegram, a messenger site particularly popular in the former Soviet Union countries and Iran, is used both for private communications and sharing information and news.
"Yesterday Telegram experienced a record increase in user registration and activity," Durov, 36, wrote on his Telegram channel.
"We welcomed over 70 million refugees from other platforms in one day."
"For the new users I'd like to say this -- welcome to Telegram, the largest independent messaging platform," Durov added.
"We won't fail you when others will."
According to monitoring firm SensorTower, Telegram has gone from the 56th most downloaded free app in the United States to the fifth.
It was founded in 2013 by brothers Pavel and Nikolai Durov, who also developed Russia's social media network VKontakte.
Telegram refuses to cooperate with authorities and hand over encryption keys, which has resulted in its being banned in several countries, including Russia.
Moscow reversed course on the app last year, however, after more than two years of unsuccessful attempts to block it.
In January, Durov said Telegram had over 500 million monthly active users and gained 25 million users in a day after a tweak to WhatsApp's data-sharing terms.