Obada Mzaik, seen in this undated family photo provided by Dr. Firas Nashef, has been missing nearly three weeks after traveling to Syria on Jan. 3, according to relatives.
A 21-year-old Syrian-American has been missing for three weeks after returning to Syria from suburban Detroit, according to a family member in Michigan.
Obada Mzaik flew to Damascus from Detroit Metropolitan Airport on Jan. 3, but wasn't seen leaving an immigration checkpoint, Dr. Firas Nashef, his uncle in Farmington Hills, said.
Mzaik, who was born in Columbus, Ohio, was planning to study civil engineering at Al-Yarmouk University.
He had been temporarily living in the Detroit area with a younger brother while taking fall classes at Oakland Community College, Nashef said.
The brother, Obaie Mzaik, 19, who was on the same flight, was not detained in Damascus, Nashef said.
"We have no idea what happened," the dentist said.
"It's horrendous because knowing what we know about the prison system over there, anything goes," Nashef told the Detroit News Monday. "The prison system and justice system over there is not very impressive."
He added that Mzaik had been detained in Syria for 37 days last year, but had not been charged officially.
The Syrian government says the country is being attacked by extremists but some civilians say the only armed gangs in the city are the security forces. NBC's Ayman Mohyeldin reports.
The State Department said it was aware of the matter and was working with authorities in Syria.
On Jan. 11, the U.S. government urged Americans to get out of Syria and to avoid any travel there.
Mzaik has citizenship in the U.S. and Syria. Nashef said the family returned to Syria in 1994 when his nephew was about 3.
"Most of his life he's been in Syria," Nashef said.
The Detroit News noted that a Facebook page, entitled "Freedom to our friend Obada Mzaik," has been set up.
It had 1,220 likes as of early Tuesday morning.
"As Syrians looking for freedom, we are outraged by the obscure circumstances surrounding Obada's arrest, and we express our deep concern over his safety in the Syrian regime's custody," the petition says.
One message, which msnbc.com was immediately unable to verify, says "because he is my son ... I want him free and now."
The Associated Press contributed to this report.