03/24/2011 at 07:35 PM EDT
All eyes are on Captain America.
But Chris Evans, who stars as the titular superhero in the upcoming action flick, was focused on one lady in particular Tuesday night at Trousdale Lounge in L.A.: Twilight
star Ashley Greene
"They were flirtatious and dancing closely together at points during the night," an onlooker tells PEOPLE of the two. "They were talking a lot and whispering."
Adds another clubgoer: "He was making her laugh, and she would push him in a flirty way." The two spent the night hanging out at tables with a large group and enjoying tunes spun by DJ Devin Lucien.
And while Greene, 24, is newly single – having recently spent time with rocker Jared Followill
in New York City after splitting from Joe Jonas
– she and Evans are not an item.
"They're both single," says a source. "They're friends. They were having fun."
The next night, Evans, 29, was spotted at West Hollywood's Chateau Marmont sans Greene – but he did attract the attention of female revelers on the patio. Once outside, the actor was quick to remove his black, fitted jacket, revealing a killer physique in his tight red T-shirt with black logos emblazoned on the chest. According to an onlooker, he was "dripping charisma yet still seemed likable and approachable."
The actor, whose Captain America
trailer was just released (watch it below), kicked back and chatted with his male companion, and he seemed to be in good spirits. Evans also turned down some of the heaters on the patio, but when he made eye contact with some female onlookers, he apologized and said they could have his jacket if they got cold.