Pals, family and motorsport stars have managed to raise more than £650,000 for the 17-year-old, from Charlwood, Surrey.
Red Bull Racing firebrand Max Verstappen has now donated a further £15,000 to the campaign on JustGiving.
Meanwhile, the teen – who has now woken from a coma – is already determined to get behind the wheel again, learning how to use a clutch on a steering wheel with his hands.
“He’s exceptionally positive about the situation – he’s sat there working out how to use a clutch on the steering wheel with his hands.”
Verstappen, the youngest race winner F1 history, forked over the cash as people from across the racing world helped out.
The Dutchman also shared the JustGiving page to his near 500,000 followers on Twitter.
The 19-year-old said: “Really shocked about Billy Monger’s terrible accident. If you can, please join me in helping him out.”
1991: posing for a photocall in Hamburg
JHR Developments driver Billy was involved in major crash at the Donington Park racetrack near Derby on Sunday.
His open-wheeler shunted into the rear of another car which had stopped in the track – with the accident broadcast live on ITV4 – and was trapped for 90 minutes.
Monger has had both of his lower legs amputated, family and friends confirmed earlier this week.
The young driver graduated from go-karts to cars in 2014 and had shown a huge amount of promise, winning a haul of trophies.
His manager told Autosport that Billy is determined to return to racing despite his horror crash.
Ralf Schumacher, Australian Grand Prix, 2002
Steven Hunter, from JHR Developments, said: “We’ve had some real positives. Billy was breathing on his own and talking, to a degree.
“He’s aware of his injuries. He’s exceptionally positive about the situation – he’s sat there working out how to use a clutch on the steering wheel with his hands.
“That’s Billy. There’s a long, long road ahead, he’s going to go through some hard times, but I’m sure with the character he has he’ll come through it.”