Police said Laila Al-Matrouk had just pulled out of her driveway on a bicycle on Sunday and was trying to cross two lanes of traffic on Route 1 when a vehicle hit her.
Her older sister said Laila suffered a traumatic brain injury and posted on social media that she was beautiful, smart, strong willed, outspoken, funny and charismatic.
Friends and school officials described Laila as kind and caring, everyone loved her and that she was a role model for her peers.
"She was an extraordinary and outspoken thinker and leader," School Superintendent Mary Alice McLean said.
"She led the civil rights team. She was working with me, the superintendent of schools, to bring Seeds of Peace to Belfast Area High School," McLean said. "She was working with Mayor Paradis to do an internship and leadership with her. She was a talented musician, talented actress. Kind, loving person."
At the middle school, counselors spoke to several students and parents trying to cope with the loss.
Laila, whose family originally is from Kuwait, spoke several languages, was active in promoting peace and went to the Seeds of Peace camp the last two summers.
The speed limit on the stretch of road on which the accident happened, near the Belfast-Searsport town line, is 55 mph.
Police don't believe speed nor alcohol are factors in the crash, which remains under investigation.
The teenager's family said she will be buried in Kuwait, where a service for her will be held when they return.