Coral, 44, appealed to the public to sign up to the Child Rescue Alert text and email system as the two mums met for the first time.
It will send out an alert when a child has been taken or is believed to be in peril.
Coral - whose daughter April was murdered by paedophile Mark Bridger in Wales in 2012 - said: "I want us to work together to make a difference."
Speaking at London's St Pancras train station, she added: "I really hope something positive can come of this."
Kate, 46, said: "There is now something we can all do to help."
Her daughter, Madeleine, disappeared from a resort in Portugal in 2007 aged three.
For more information on Child Rescue Alert, visit Childrescuealert.org.uk.