Britain's Got Talent: Birmingham saxophonist Julian Smith in semi final
Judge Simon Cowell offered the 46-year-old Ghost star two first class tickets for her and her husband Ashton Kutcher to fly to Britain for the grand final on Saturday night.
Moore agreed to jet over after being approached by judge Amanda Holden on the micro-blogging website Twitter.
Asked if she would fly over from Los Angeles if Cowell offered her the use of his private jet, Moore wrote: "Well if he offers the ride..."
Later, Holden wrote: "Message for Demi!! Please someone get this to her as I am still rubbish at twittering Simon says Yes!! But to first class tickets!!! Xxxxx"
Moore, who has more than a million followers on the site, joked: "what no private plane? lol Generous offer! Thank you! And thank Simon! When are the finals?"
The actress first backed Boyle, 48, of Blackburn, West Lothian, after seeing her sing I Dreamed A Dream from Les Miserables during the auditions.
Comedy dance act Stavros Flatley won Tuesday's public vote to secure a place in the final, with father-and-son performers Demetrios and Michalakis Demetriou, from north London, dancing to Zorba The Greek.
They will be joined by singer Shaheen Jafargholi, 12, from Swansea, who was reduced to tears when he was saved by the judges' vote.
A total of 10 acts will be chosen to compete in the final and dance groups Flawless and Diversity and singer Shaun Smith are the other finalists so far.
The hopefuls will compete for a prize of £100,000 and a chance to perform in front of the Queen at the Royal Variety Performance.
