An image released believed to be of Constance Marten in Essex has been released by police.
Essex Police is now leading the search for the couple, both originally from London, and their baby.
Det Ch Insp Rob Huddleston said police "do not wish to interrupt their family life - this search is primarily to ensure the welfare of the couple's child. "We are carrying out a number of inquires in and around Colchester in order to locate them. We're also liaising with colleagues at British Transport Police around potential onward travel from Colchester.
"I would ask the people of Colchester, and indeed wider north Essex, to please familiarise yourself with Mark and Constance's faces and report any sightings to us immediately."
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