First, Apple and Google removed the app from their app stores because they said it had not sufficiently policed its users’ posts, allowing too many that encouraged violence and crime. Then, late Saturday, Amazon told Parler it would boot the company from its web-hosting service on Sunday night because of repeated violations of Amazon’s rules.

Amazon’s move meant that Parler’s entire platform would soon go offline unless it was able to find a new hosting service on Sunday.

“Big tech really wants to kill competition,” John Matze, Parler’s chief executive, said in a text message. “And I have a lot of work to do in the next 24 hours to make sure everyone’s data is not permanently deleted off the internet.”

A day earlier, Parler appeared poised to capitalize on growing anger at Silicon Valley in conservative circles and was even a logical choice to become Mr. Trump’s next megaphone after he was kicked off Twitter. Now its future is looking bleak.