The Saturday Night Live actress was spotted cosying up to the Strokes drummer at the New York City launch party for The Black Keys' new album on Monday.
An eye-witness told Us Weekly: "Kristen and Fabrizio were making out in a booth. They were all over each other! They were definitely not discreet."
The pair were spotted by another insider as they partied together again two nights later.
Wiig has been linked to filmmaker Brian Petsos and was also previously married to actor Hayes Hargrove for four years.
Moretti began dating Barrymore in 2002 after meeting her at a Strokes gig, but the couple separated in January 2007.
Representatives for the two celebrities haven't commented on the report.
Wiig will appear on this weekend's edition of Saturday Night Live, with host Katy Perry and musical guest Robyn, airing at 11.30/10.30c on NBC.
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Watch Kristen Wiig in a sketch from Saturday Night Live below: