Liam Colgan, 29, from Inverness, vanished in the early hours of Saturday.
He had organised the trip to the German city with his brother Eamonn, 33, a policeman, who was supposed to be getting married in two weeks’ time.
They arrived in the the city on February 9 and visited a few bars, including the Hamborger Viermaster which was the last place they were in.
Police in Hamburg have launched a search for Liam while his friends have set up a Facebook page.
In a post on Friday they said there have been fresh sightings of a Scottish man.
The post said: “There have been further sightings of a CONFUSED man saying he is from Scotland.
“We really need your help now to try and narrow down the search. If you see him please assist him and contact Hamburg police on 040 4286 56789 or 110.”
They are urging people to put up posters of Liam in Buxtehude, Hamburg and all surrounding areas.
Dundee United captain Willo Flood also made a video appeal.
Eamonn raised the alarm on Saturday when he woke up and discovered his brother was not in the room they were sharing.
He called police in Hamburg who have since been in contact with hospitals and taxi companies and have interviewed witnesses.
Search dogs have also been used and Liam’s picture circulated online and to media outlets.
Eamonn has said the wedding will not go ahead without his brother.