Former Trump adviser Jason Miller says a new, free-speech-focused social-media platform he is leading has received financial backing from a foundation tied to fugitive Chinese businessman Guo Wengui.

Called Gettr—a portmanteau of “getting together”—the Twitter -like platform appeared in app stores last month and will formally launch on July 4, Mr. Miller said.

Mr. Miller, who recently left Mr. Trump’s office to serve as chief executive of the venture, said Gettr—registered in Delaware and headquartered in New York—was backed by international investors that include “the Guo family foundation.” He added Mr. Guo doesn’t have a direct financial stake or direct role in Gettr, nor did he identify the foundation that made the investment.

The Wall Street Journal wasn’t able to independently identify the foundation, and Mr. Miller didn’t comment further on it.

In an online video last week that was viewed by the Journal, Mr. Guo said he was an adviser to the social-media platform but wasn’t involved as a member of its management. An account under the name of Mr. Guo, an avowed critic of China’s Communist Party, that is marked as verified by Gettr indicates that it was set up in July 2021.