A Nottinghamshire man has returned from Austria after spending several weeks searching for his missing son.
Christopher Miles, 28, was working as a tour guide near Salzberg when he went missing on 31 July.
His family, who say he was depressed, believe he could have suffered an adverse reaction to medication and be "wandering Europe somewhere".
His father Nick Palmer-Miles flew out to speak to Austrian police and media but said he "still knows nothing".
On the day he went missing, Mr Miles, from Langar, travelled from his apartment in Zell am See to Salzberg Airport, where he drove a group of tourists across the border to Ruhpolding in Germany.
His minibus was found near Ruhpolding station, unlocked and with its lights on.
Mr Palmer-Miles, who works as a firefighter in Leicestershire, said: "He had had a conversation with somebody in Ruhpolding which was in German, and that was the last guy to see where my lad was.
"He said he looked very agitated and then my son just disappeared and from this day we don't know where he is."
Mr Palmer-Miles flew out and reported his son missing to police, and has also spent weeks handing out missing person leaflets.
He added: "It was very difficult because at the end of the day I've just had to go over there and shut my son's life down for him.
"It could be one of two things. My son could have died four weeks ago.
"There's also a chance he may have lost his mind and he's out somewhere wandering Europe. And the moment we don't know."
A Facebook page set up to help find Mr Miles has attracted more than 4,000 members.