"The whole family is highly concerned for his well-being," the family of Josh Sanchez-Maldonado said in a written statement, later adding in a video released by police that their son is a "very lovable person, very communicative and outspoken."
"Let him know that we're concerned and that we love him very much," his father, Jose Sanchez, says in the video, speculating that he might be lost and pleading for Londoners to take good care of him.
The 24-year-old U.S. national, who's based in San Francisco, had arrived in the U.K. on his first solo trip outside the United States, police said. A trader by profession, he was in London for a job interview and was staying at the St. Giles Hotel in Feltham.
Sanchez-Maldonado was due to fly to San Francisco via Dublin Oct. 22 but police say he was not on the flight back.
"Officers are increasingly concerned for Josh Sanchez-Maldonado," London's metropolitan police said in a statement.
The family said they had "kept in close communication" since their son had arrived in the U.K. but have not heard from him since Oct. 21.
Reached by ABC News, the U.S. Embassy in London said that they were aware of the young man's disappearance and said they were working closely with his family and British police.