The family of missing teenager Mariam Makhniashvili will be celebrating her birthday Tuesday with a cake and 18 candles, all the while wondering where she could be.

Mariam's father, Vakhtang Makhniashvili, her mother, Lela Tabidze, and her 16-year-old brother George will likely spend the rest of Mariam's birthday in silence and looking at old photos of her and focusing on positive prayer.

"It's a very unusual birthday but we will try to keep good thoughts and sit together and remember," Tabidze told CTV Toronto.

The teen disappeared Sept. 14 while walking to Forest Hill Collegiate school with her brother. She told him that she would be going in the front door because it was closer to her first-period class -- and then seemingly vanished.

Mariam's parents revealed today that a police polygraph test proved the boy was telling the truth about his sister's disappearance.

The family and Toronto police are still trying to solve the mystery behind her disappearance. Police have no evidence of foul play or that she even ran away.

They have reached out to the community by appearing at two high schools in the area where the girl's backpack -- loaded with her school books -- was found by a passerby on Oct. 8, behind an apartment on Eglinton Avenue East, more than two kilometrrs east of her school.

Meanwhile, Mariam's parents have dismissed rumours that she ran away because she left home with no extra money, clothes or a passport, and running away would be out of character for Mariam. They also said the teen has not tried to contact friends or relatives back in her native Georgia, and had no close friends in Toronto.

Their children left Georgia in June to reunite with their parents, who had lived in Los Angeles for the past five years.

Today, the girl's parents cling to hope that Mariam is alive and being held against her will.

"That is our biggest hope, that somebody out there knows something," said Tabidze.

Mariam is white, 5'3" with light brown, shoulder-length hair and brown eyes. She was last seen wearing black jeans with front and back pockets and buttons as well as a baby blue, long-sleeved v-neck shirt. She was wearing a waist-length blue jean jacket.

People with information are asked to contact police at 416-808-5300, Crime Stoppers anonymously at 416-222-TIPS (8477), online at www.222tips.com, or text TOR and a message to CRIMES (274637).

With a report from CTV Toronto's Jim Junkin