The move potentially opens up new revenue streams to Twitter, which has struggled to expand its user base.
Twitter has some 320 million active users, but claims its "total audience" is much larger, with many more people viewing tweets without joining or logging in.
Twitter product manager Deepak Rao said the new feature would be "a test for marketers to reach the over 500 million people who visit Twitter each month to keep in touch with what's happening without logging in."
We've launched a test that enables select advertisers to extend their marketing campaigns to our logged-out audience https://t.co/YxdlubEArr
— Marketing (@Marketing) December 10, 2015
Twitter's 'favourite' stars become 'like' hearts
Rao said this "includes people who click on links to Tweets in Google search."
Much of Twitter's revenues come from ads known as "promoted tweets."
The company, which recently brought co-founder Jack Dorsey back as chief executive, has never made a profit.
Twitter shares jumped 6.5 per cent on the news to $25.89.
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