Mr Abdulmutallab is from a wealthy Nigerian family
The family of a Nigerian man charged with trying to blow up a transatlantic jet on Christmas Day says his actions are "completely out of character".
They said that, until recently, Umar Farouk Abdulmutallab, 23, had never given them cause for concern.
His father, a prominent banker, alerted security agencies about two months ago when his son broke off communication.
Meanwhile, the UK said on Monday that Umar Farouk Abdulmutallab had been on its security watch list.
This meant he could not come into the UK, although he could pass through the country in transit.
Home Secretary Alan Johnson said he had been refused a visa 14 months ago after applying to study at a bogus college.
The Abdulmutallab family, based in Abuja, said that they "like the rest of the world were woken in the early hours" of 26 December to the news of their son's alleged attempt to blow up a flight between Amsterdam and Detroit.
They said that prior to this event, his father, "having become concerned about his disappearance and decision to break off communication while schooling abroad", had approached security officials in Nigeria and overseas.
"We were hopeful that they would find and return him home," the statement said. "It was while we were waiting for the outcome of their investigation that we arose to the shocking news of that day."
The statement went on to say that the recent disappearance and end of all communication by their son was "completely out of character and a very recent development".
Until then, "from very early childhood, Farouk, to the best of parental monitoring, had never shown any attitude, conduct or association that would give concern".
"As soon as concern arose, very recently, his parents reported it and sought help."
The statement went on to say that the family would fully co-operate with any investigation, and gave thanks "that there were no lives lost in the incident".
The BBC's Caroline Duffield in Lagos says the suspect's father, Alhaji Umaru Abdulmutallab, is a prominent banker well-connected in Nigeria's political world.
UMAR FAROUK ABDULMUTALLAB
Son of a wealthy Nigerian businessman
Attended a British school in Togo
Studied mechanical engineering at University College London
Spent time in Dubai, Yemen and Egypt
He is said to have approached the US embassy in Abuja in November to voice concerns about his son, who is a former engineering student at University College London.
The family have told the BBC Hausa service that they lost contact with Mr Abdulmutallab in October, when he was living in Yemen.
Mr Abdulmutallab's route began in Yemen, from where he travelled to Ethiopia, Ghana and Nigeria. On 24 December, he flew from Lagos to Amsterdam, where he boarded the flight to Detroit.
His name was on a security database of more than half a million individuals, known as Terrorist Identities Datamart Environment (Tide), but there was not enough information about his activities to place him on a blacklist that would have prevented him from flying.