Just nine seaside towns, all in the south west or south east of England, are served by an association member who lists that area as their primary place of work. These are Brighton, Worthing, Bournemouth, Poole, Penzance, Redruth, Plymouth, Portsmouth and Weston-Super-Mare.
Young people in coastal towns in Northumbria, Essex, Kent and Cornwall may have some limited access through outreach psychotherapists based nearby, the ACP said.
However, the Yorkshire, Lincolnshire, East Anglia, Lancashire, Cumbria and Wales coastlines have no access to child and adolescent psychotherapists.
The ACP evidence has been submitted to the House of Lords select committee on regenerating seaside towns, which launched in May to examine the distinct challenges facing coastal communities.
Seaside towns have a particularly high prevalence of mental illness among children, due to deprivation and the high number of looked-after children placed in such areas by local authorities, according to the ACP.
"It is known that some seaside towns are particularly affected by deprivation and poverty," states the ACP evidence.
It adds: "There are particular concerns for the wellbeing of children and young people who are looked-after, either in foster care or children's homes.
"The prevalence of mental illness is significantly higher in looked-after children than equivalent populations. At the same time many coastal districts have significantly higher populations of looked-after children.
"Out-of-area placement of looked-after children is common in England, despite the law insisting that it should only be done in exceptional cases and only for reasons that expressly benefit the child.
"Numbers placed in residential homes outside their local authority area increased by nearly two-thirds in five years.
"Many of these vulnerable children end up in seaside towns because of the availability of relatively cheap accommodation that residential child care providers can turn into children's homes and offer low-cost placements for local authorities with limited resources."
Dr Nick Waggett, ACP chief executive, said rural areas also suffer from a lack of access to child psychotherapists, who are available mainly in urban areas and the south of England.
He is calling on the government to ensure that all areas have good access to specialist support.
"We have just written to Health Secretary Matt Hancock asking for him and NHS England to implement a national plan around children's psychotherapy to require all services to provide access to child psychotherapy," he said.
The Department of Health and Social Care has been contacted for comment.