Scarlett Johansson `engrossed in Justin Bartha`

After her break-up with Sean Penn the Lost In Translation actress has been spotted getting very cozy with Hangover star Justin Bartha.

Johansson, who separated with Penn four weeks ago, was at the launch of the Manhattan stage show All New People that Bartha is appearing in.

On Saturday the high-flying pair were photographed together backstage.

Witnesses told the US media that Johansson and Bartha were 'completely engrossed in each other' during a special dinner for the cast that also attended by playwright Zach Braff and actress Heather Graham at Café Un Deux Trois in New York City.

One witness said, 'There were about 15 people at the table, Scarlett and Justin sat next to each other and talked all night.

'They seemed really fascinated with each other and only talked to each other,' the source said.

'It looked sometimes flirty, but also they seemed to be involved in a deep discussion.'

While some claiming that Johansson, 26, and Bartha, 33, are just good friends the pair were also reportedly seen 'flirting up a storm' at a New York Karaoke bar on Saturday.

Her five-month fling with 50-year-old Penn ended in June. Bartha ended a two-year relationship with Ashley Olsen in March.

Scarlett's ex-husband Ryan Reynolds has recently been linked to Charlize Theron but was spotted on a New York rooftop bar on Tuesday chatting to an attractive woman while with a group of friends.

A witness said, 'I definitely got the vibe that Ryan had eyes for a brunette. All four hung out the entire time together, but there was definitely chemistry between the two them. Lots of laughing and all smiles.'

Reps for Johansson and Bartha didn't comment to the US media. Ryan Reynolds' rep said, 'No comment'.