The London Stock Exchange (LSE) has suspended trading in the VK Group, the Russian media company which is 25.7% owned by Naspers subsidiary Prosus.
The VK Group owns Russia's biggest social media network, VKontakte.
On Thursday, the LSE said it was taking the action "further to recent sanctions in connection with events in Ukraine" and to "maintain orderly markets".
The exchange also suspended trading in 26 other Russian companies, including state-owned gas company Gazprom, oil giant Rosneft and aluminium producer EN+.
Naspers bought a stake in VK – then known as Mail.ru, in 2006. It listed in the LSE in 2010.
Before trading was suspended, the media group's shares had plunged to under $1 as investors shunned Russian stocks.
Earlier this week Prosus refused to be drawn on the future of its stake in VK. "We hold a minority stake in VK, which is publicly listed on the London Stock Exchange. VK is controlled and run in Russia," it said.
VK Group's CEO, Vladimir Kiriyenko, was last week sanctioned by US authorities as a "Kremlin-connected elite" close to Russian President Vladimir Putin.
* Fin24 is a subsidiary of Media24, which is part of Naspers.