Security upgraded after passengers injured and carriage windows smashed.
Eight Auckland commuter trains have had windows smashed by rock-hurling vandals, injuring passengers in one case.
Rail operator Transdev and Auckland Transport have stepped up security between Avondale and New Lynn on the western line after the trains were hit in attacks on Saturday and on Monday evening.
Police searched long grass in an empty section off St Georges Rd, Avondale, for three young men seen after Monday's attacks.
They did not find the suspects but are continuing an investigation into the attacks.
Some trains were still travelling the rail network yesterday with smashed windows taped up from the attacks. One train was seen on the western line with four smashed windows, and another with two.
Two passengers travelling west on a crowded train about 6.40pm on Monday were left with minor injuries from broken glass, said Transdev, which is contracted by Auckland Transport to run the city's passenger rail services.
Another passenger on the train told the Herald he heard a "huge bang" as glass shattered in the large window of an outside door to his carriage.
He said a train attendant told him a rock had gone right through a window in the next carriage.
Transdev managing director Terry Scott said the company and Auckland Transport had boosted security patrols in the area, and were working closely with police.
"Antisocial behaviour such as rock-throwing does unfortunately happen on rail occasionally, as it does on roads, and Transdev is committed to preventing and prosecuting this kind of behaviour," he said.
The incidents follow attacks about three weeks ago on rail staff on the western line that left one worker with a broken jaw and another with a fractured eye socket.
A 20 year-old man has appeared in court on a charge of wounding a KiwiRail worker on a train near Avondale Station and five boys, aged 13 and 14, were referred to the police youth aid section after attacks several days later on two Transdev staff at Ranui and Swanson.
Mr Scott said at the time that the company was considering civil proceedings against offenders, in addition to criminal prosecutions by police.