The 49-year-old actress, who split from Ashton Kutcher earlier this year, was pictured with Henderson in Connecticut last week.
According to Life & Style magazine, Demi and Martin - who is 12 years her junior at 37 - stayed at a vacation home together.
They went out for romantic lunches and dinners during their holiday and onlookers described Demi as being 'flirty' in his presence.
The pair were spotted dining at local restaurants and heading to a barbeque with friends together.
An onlooker described them as "very comfortable with each other".
Henderson appeared in Shortland St and Australian soap Home And Away before embarking on a movie career in the US.
He appeared in Britney Spears' steamy Toxic video in 2004, and has a starring role in thriller The Moment, set for release next year.
Moore has undergone highly publicised struggles since her marriage to Kutcher crumbled.
She went to rehab in January after inhaling nitrous oxide, where she reportedly received treatment for substance abuse and anorexia issues.
It was reported that Moore was 'devastated' over Kutcher's blossoming romance with his That 70's Show co-star Mila Kunis.
However, the recent pictures of her with Henderson tell a different story.
