Pierre Omidyar, the founder of eBay, has revealed more details of the media organization he is creating with journalist Glenn Greenwald.

Greenwald announced on Tuesday that he was leaving the Guardian, where he has broken a series of stories on the National Security Agency, based on documents from whistleblower Edward Snowden.

In an interview with Jay Rosen, media critic and NYU professor of journalism, Omidyar said he was committing an initial $250m to the as-yet-unnamed venture. Omidyar told Rosen the decision was fuelled by his “rising concern about press freedoms in the United States and around the world”.

Omidyar said he hopes the project will promote “independent journalists with expertise, and a voice and a following” while using Silicon Valley knowhow to build an audience. “Companies in Silicon Valley invest a lot in understanding their users and what drives user engagement,” Omidyar said. The company will be online only and all proceeds will be reinvested in journalism.

In a blogpost, the eBay billionaire revealed that he had been exploring a purchase of the Washington Post, which was ultimately bought by Amazon founder Jeff Bezos.

“That process got me thinking about what kind of social impact could be created if a similar investment was made in something entirely new, built from the ground up. Something that I would be personally and directly involved in outside of my other efforts as a philanthropist,” wrote Omidyar.

“I developed an interest in supporting independent journalists in a way that leverages their work to the greatest extent possible, all in support of the public interest. And, I want to find ways to convert mainstream readers into engaged citizens. I think there’s more that can be done in this space, and I’m eager to explore the possibilities,” he wrote.

Omidyar said he was in the “very early stages of creating a new mass media organization. I don’t yet know how or when it will be rolled out, or what it will look like.” He said the organization would cover general news as well as investigative journalism.

“As part of my learning process, I recently reached out to Glenn Greenwald to find out what journalists like him need to do their jobs well. As it turns out, he and his colleagues Laura Poitras [video documentarian] and Jeremy Scahill [author and national security expert], were already on a path to create an online space to support independent journalists. We had a lot of overlap in terms of our ideas, and decided to join forces,” wrote Omidyar.

“I have always been of the opinion that the right kind of journalism is a critical part of our democracy,” he told Rosen.