Emergency services were alerted about 4pm and went directly to Taita station but the pair had gone.
Today a police spokesman said police were working with KiwiRail and the Greater Wellington Regional Council's rail monitoring centre.
"[This is] to review all CCTV footage they have captured in the hopes of identifying the two people that were on the front of the train."
He said police were trying to establish exactly where the pair got on, and got off, the train.
"We are still appealing to witnesses to come forward with any information - we certainly want to talk to these two people about their actions."
Last year there were 418 reported incidents of trespassing on the rail corridor nationwide, an increase of 103 on 2013.
KiwiRail reminded people that it was considered trespassing to cross or walk along railway tracks at any place other than a designated level crossing - that included riding the back of a train.
Anyone found to have trespassed would be required to pay a fine.
A KiwiRail spokesman said under the Crimes Act it was illegal to enter or climb onto a vehicle - which in this case would be the rail carrier.
These charges were punishable by up to two years in prison, he said.
KiwiRail general manager of metro David Shepherd said he was "astounded" to see the two young men put their lives at such risk.
Mr Shepherd said KiwiRail were assisting police with their investigation.
"We will be doing everything we can to help police identify these two young men and strongly urge anybody considering trespassing on the rail corridor to think about the value of their life and how their families will feel if they are killed or injured."