The hooded teenagers smashed more than 100 windows at private hire firm AC’s Taxis & Minibuses in Tranent during a brazen Sunday afternoon raid.
They were captured on CCTV using gas canisters, bricks and fire extinguishers to target the fleet, which is often used to take local children to school.
Staff believe the carnage would have been far worse had the youths not been disturbed by a mechanic from a nearby garage.
Robert Campbell, a partner in the business, has revealed the firm is now offering a £5000 reward to anyone who provides information leading to prosecution.
He said: “We have had windows smashed before but nothing this serious. The damage is unbelievable.
“It’s not just the odd window. It’s every window on almost every vehicle as they worked their way down.”
Police have launched an appeal for witnesses following the incident, which happened between 2.30pm and 3.30pm on Elphinstone Road.
They said two, and possibly three, suspects aged 13 to 16 had vandalised almost 30 vehicles using various items to smash the windows. The teenagers were dressed in black with their hoods up, while one had collar-length black hair. CCTV footage shows them walking up Elphinstone Road and gaining access at the back of the fleet compound.
One of the group is seen entering a small coach before something appears to startle him. He is then seen quickly leaving the vehicle and sprinting back up the way he came.
Mr Campbell said a man parked in a silver Nissan, also captured on CCTV, may have seen the teenagers pass by his car.
Alan McDonald, the mechanic who disturbed the teenagers, said he heard a “couple of bangs” but did not see anything suspicious during the raid.
Sergeant Derek MacDonald said: “This was a senseless act of vandalism which has caused considerable damage and I’m urging anyone who can assist with our enquiries to come forward.”
David Forrest, vice-chairman of Tranent community council, said he was “shocked” so much damage could be caused in broad daylight. Anyone with information on the attack is asked to contact police on 101.