Previously he worked for the Canadian foreign service, where he had risen to be vice consul at the embassy in Beijing. He is a well-known specialist on East Asia and Chinese foreign policy.

“We are aware of the situation of the Canadian detained in China,” Mr. Trudeau told reporters on his way into the House of Commons in Ottawa.

“We have been in direct contact with the Chinese diplomats and representatives,” he said. “We are engaged on the file, which we take very seriously and we are, of course, providing consular assistance to the family.”

The Chinese Ministry of Foreign Affairs had no immediate comment.

Two friends of Mr. Kovrig’s in Beijing said they had been unable to reach him by phone or email. Both requested that their names not be used, fearing unwelcome attention from the Chinese authorities. Calls to Mr. Kovrig’s two cellphone numbers went unanswered.

Mr. Kovrig’s last activity on his Twitter account, a retweeted comment, appeared on Sunday.

“I am not willing to speculate as to the reason why the Chinese authorities chose to do what they did. I am willing to state categorically what is not the reason for Michael’s detention. He did not engage in illegal activities. He was not endangering Chinese national security,” said Rob Malley, president and chief executive of the International Crisis Group. “He was doing what all Crisis Group analysts do: objective and impartial research and policy recommendations to end deadly conflict.”

It is unclear whether Mr. Kovrig’s disappearance is related to his work for the crisis group. He specialized in sober analyses of North Korea, tensions over the South China Sea, China’s involvement in international peacekeeping and other diplomatic issues.