The 'Rum Diary' co-stars - who have been romantically linked since Johnny announced he had split from his long-term partner Vanessa Paradis - couldn't keep their hands off each other as they enjoyed an evening in the VIP section of Los Angeles' AV Nightclub.
A source told the New York Post newspaper: ''They looked very flirty and sat close, conversing the whole time.''
It was recently revealed the couple were dating again after Johnny wooed Amber back with handwritten poems and flowers.
The 49-year-old actor - who confirmed his split from the mother-of-his two children Vanessa in June - enjoyed a brief romance with the actress in the summer after meeting on the set of 'The Rum Diary'.
But Amber ended their romance after deciding she wanted to be single.
However, Johnny decided not to give up on the 26-year-old beauty and sent her a personally penned poem and a bouquet of roses every day throughout September to convince her to give him another chance, and his plan eventually worked and she flew out to his private island, Little Hall's Pond Cay in the Bahamas, for a mini vacation.
A source said: ''Johnny didn't give up - he missed her so much over the summer. They both love literature and the way he tried to win her back totally worked.
''Once they flew to his island in the Bahamas for a romantic break a couple of weeks ago, they were back on as a couple. Johnny's the type to fall hard and he's vowed not to let a girl like Amber, who's beautiful and intelligent, slip through his fingers.''