On Thursday, they lost their jobs, as Joe Ricketts, the billionaire founder of TD Ameritrade who owned the sites, shut them down.

At 5 p.m., a post by Mr. Ricketts went up on the sites announcing the decision. He praised them for reporting “tens of thousands of stories that have informed, impacted and inspired millions of people.” But he added, “DNAinfo is, at the end of the day, a business, and businesses need to be economically successful if they are to endure.”