The teenagers, named locally as Dominic O'Neill, Kyle Warren and Billy Hines, died in Tivetshall Road, near Pulham Market, Norfolk, on Wednesday night.
On Thursday, hundreds of people gathered at Eye airfield to remember them and release lanterns.
"It was an unbelievable night," said Adam Kerry, a friend of Mr O'Neill.
Mr O'Neill, 18, and Kyle, 17, were from Harleston, while 16-year-old Billy was from Wortham in Suffolk.
They died at the scene after the car burst into flames. A number of bunches of flowers have been left at the roadside in their memory.
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Archbishop Sancroft High School in Harleston said the whole school community had been left "shocked and saddened" by the news of their deaths.
Two of the teenagers were pupils at the school, which opened its doors during school holidays to offer support to those affected by the deaths.
A book of condolences is also available to sign at St John's Church in Harleston.
The Reverend Nigel Tuffnell said: "It is just one of those things you don't expect ever to happen and you hope and pray that it doesn't happen.
"Unfortunately it has happened and it's happened to three families."
Friends of three teenage boys killed when the car they were in crashed into trees have gathered to release Chinese lanterns in their memory.