Leominster -- The state fire marshal's office is investigating the death of a 16-year-old Leominster boy who was killed when his home became engulfed in flames Wednesday night.

He was identified as Jakob Chessborough, a student at Leominster High's Center for Technical Education.

His friends and classmates gathered Thursday to mourn their friend, who they said was affectionately nicknamed "Cheeseburger."

"He never caused any trouble. Never. And if there was trouble, he would be the one to fix it," a tearful Mariah Saseen said.

"I loved him to death," his friend Blake Goodwin said.

Fire officials said Chessborough was overcome by smoke in a third-floor bedroom when flames broke out in his multi-family home at 179 West St. in Leominster around 11 pm.

The fire was so intense that Chessborough's 13-year-old sister, Katie, was forced to jump from a second-floor balcony to escape.

His 15-year-old sister, Tori, had to be rescued from a room on the second floor by firefighters.

"The bed was next to the window. We couldn't see a hand in front of my face. It was that black in there, the smoke was right to the floor. And if it wasn't for her crying I never would have never saw her," said firefighter Scott LaPrade said.

Both were awakened by the sound of smoke alarms going off. A neighbor called in the alert on the two-alarm blaze to the fire department.

"The crews got here. Some passersby had already taken a young lady off the front porch. There was another young lady -- a teenager -- hanging out the window on the side of the building. Put a ladder up, took her out. And the crews went to work and a young male was found on the third floor -- teenage male -- and he had succumbed to his injuries and smoke," Deputy Chief Al Kirouac said.

Both girls were expected to be OK. Their mother was at work at the time and a couple who lives on the first floor was also uninjured, officials said.

For Jakob's friends, it will be some time before they recover from the shock.

"He was loved. He gave the world to everybody around him," Goodwin said.

The cause of the blaze is under investigation. Fire investigators said it appeared to start in the back of the second floor.

Mayor Dean Mazzarella has established an account with Fidelity Bank to assist the families devastated by the fire.

Donations can be made payable to the City of Leominster Relief Fund and mailed or delivered to Fidelity Bank, 9 Leominster Connector, Leominster, MA 01453, c/o Katy Kirouac.