The reality TV star - who has previously dated models Kimberly Stewart and Niki Cloyd - was spotted celebrating his 25th birthday early in Las Vegas on 06.11.10 by cosying up to blonde Sarah McNeilly at the 5th anniversary of TAO restaurant and nightclub.
An onlooker told Life and Style magazine: "Sarah was there as Jack`s date. He took her to Vegas to celebrate his birthday with him."
Jack, who turned 25 on 08.11.10 and the American model - who is signed to Select Model Management - are said to be smitten with each other.
The source said: "TAO presented Jack with a birthday cake, and Sarah was by his side when he blew out the candles. They`re very much on, full speed ahead. They seem super into each other! Both seem very happy."
Although Jack recently admitted he thinks British women are more naturally beautiful than American girls, he revealed he appreciates different qualities in women from both countries.
He explained: "If you`re going for au natural beauty, the UK is the best place. But if you want a bit of plastic fantastic and a touch of enhancement, then America is better.
"I don`t mind whether a girl is from the UK or US."