The No Strings Attached star, who is expecting her first baby later this year, is pairing up with the Free The Children charity to launch The Power of a Girl fundraising scheme.
The organisation has urged supporters to set up events to raise the cash needed and Natalie has offered a special prize to reward the most successful fundraiser.
The 29-year-old has donated a dress she wore last year to the American Film Institute gala premiere of hit film Black Swan and she is also offering a trip to Kenya for the winner.