AfriLeaks will give people a chance to leak sensitive information anonymously.
The site's founders say it is an attempt to boost investigative journalism to expose widespread corruption and human rights abuses.
It will also help circumvent growing surveillance by governments and corporate firms, they say.
Afrileaks, made up of 19 media outlets and activist groups, says it is committed to "speaking truth to power".
"You will be able to send us documents and select which of our member organisations should investigate it," it says.
"We've designed a system that helps you to share these materials while protecting your own identity, so that it becomes impossible to identify you as the source of the leak."
Most of the 19 are newspapers and include South Africa's Mail & Guardian, Kenya's Daily Nation and Nigeria's Premium Times.
The Mail & Guardian says AfriLeaks is modelled along the lines of Europe's GlobaLeaks with the aim of making whistle-blowing safer.
"In the post-Snowden world in which we live, with government and corporate surveillance a reality, it has become critically important for journalists and whistle-blowers to take every precaution to ensure their digital safety," the paper reports.
The US wants to put ex-security contractor Edward Snowden on trial for leaking to the media in 2013 details of mass surveillance programmes. He is exiled in Russia.
Correspondents say newspapers in multi-party democracies in Africa have often exposed corruption and human rights abuses.
The challenge AfriLeaks faces is to get whistle-blowers in repressive states like Eritrea and Sudan, where control over the internet is tight, they say.