Gardaí appeals to witnesses about alleged assault on the train last week.
The teenager was stabbed in the chest during the incident and was treated in the hospital because of injuries that did not threaten life.
Another mature man was arrested at the scene and then released without charge.
Gardaí now appeals for witnesses to the incident at the Killester Dart station at 10pm on Tuesday, October 30.
They ask passengers at 21.40 of the train from Connolly Station to Drogheda to contact Raheny Garda Station on 01-6664300.
"We also ask anyone who has recorded a recording on their phones or devices to get in touch with the Garda Station in Raheny," they added.
It is understood that the victim and his attacker are known to each other.
Bus and railway drivers warn that they can use antisocial hotspots after the attack.
The National Bus and Railworkers Union warns Transport Minister Shane & Ross and Justice Minister Charlie Flanagan about a possible disruption to the stabbing service.
General secretary Dermot O & # 39; Leary said that anti-social behavior and an open bandit has reached a critical point.
He said it could only be a matter of time before staff were forced to review potential preventive measures.
This includes evaluating the provision of services at "specific hours and locations".
"In such a review, the safety of commuters and employees would be the most important" – said the letter to the ministers.
He said it looks like it will not be over a week without another headline appearing on different media platforms, which underlines another attack on our public transport system.
He called on the ministers to immediately commit to establishing a public transport branch in Garda.
"The mood among transport workers has changed dramatically due to the recent attack on our train and buses," he said.
"Although initially encouraged by the Minister's initial response, they now believe that they may have to take their own preventive measures, including assessing the provision of services at specific hot spots and in areas with high incidences of adverse reactions."
Reacting to the incident, Aodhán Ó Ríordáin, a senator from the Labor Party, also said that the latest violent incident demonstrates the need for a dedicated transport police.
"This is the latest from a long list of disturbing incidents on the Northside line, where many stations are regularly destroyed, and DART is taken over by hooded young people in the summer, trying to spray paint on a Clongriffin wagon," Senator Ó Ríordáin said in a statement.
"I am pleased that Minister Ross has expressed the will to explore the possibility of setting up a police transportation service, and the proposal must be implemented as soon as possible to ensure the safety of commuters and employees of our public transport system."
In an interview with Independent.ie, Dermot O & # 39; Leary, Secretary General of NBRU, he said: "NBRU has been calling for a split of public transport in Garda for some time now." Twice we wrote to minister June and July this year after the attack on Connolly Station.
"The initial reaction of the minister was encouraging for employees, but everything has gone forward since then – there is no week when we do not read the next headline about anti-social behavior or in some cases of open banditry on trains.
"The day is coming if we are not here yet, when employees have to take their own preventive measures, and this may include checking services at particular access points and locations where there is a type of antisocial behavior." This day is probably already here. "