The "Don't You Forget" Valentine's Day campaign will send out images of the three missing youngsters to businesses and public sites across Spain and its islands. It is hoped the posters will be displayed in banks, schools, churches, stations and other prominent places.
Two A3-size posters have been produced - one depicting Madeleine, alongside five-year-old Mari Luz Cortes, and one showing her with seven-year-old Yeremi Vargas.
Mari Luz went missing on January 13 this year in her home town of Huelva, 120 miles from Praia da Luz - where Madeleine went missing last May.
Yeremi Vargas disappeared from his home in Gran Canaria on March 10 last year.
A letter in Spanish will accompany the posters, explaining their purpose and giving information on how to contact the authorities for those who believe they can help.
In all, some 17,400 packs have been produced, costing the Find Madeleine Fund £3,000. An email version is also being sent out to thousands of recipients. The new campaign comes as the Portuguese police investigation into Madeleine's disappearance draws to a close.