Liam, 29, from Inverness, vanished in Hamburg in the early hours of Saturday.
His brother Eamonn said footage had been picked up of him walking alone.
Speaking to reporters in Germany, he said: “There have been a couple more potential sightings that the police are currently working on and reviewing CCTV on those areas.
“There is a recording of Liam in the Reeperbahn area.
“It isn’t actually outside the pub. It’s further along the Reeperbahn towards the train and subway stations.
“After that there is no other image of Liam. I don’t know the exact location. It’s some sort of gaming area, I think he was outside there.
“He is seen walking alone, as we thought he would have been.
“We don’t know much more at this time.”
He earlier spoke to BBC Radio 1’s Newsbeat programme and pleaded with his brother to get in touch.
He said: “Please, please come home. Everyone misses you.
“You’re very much loved. I don’t know what happened to you, just please get in touch, find a way.”
Eamonn, 33, was supposed to be getting married in two weeks’ time and Liam had organised the trip to Hamburg and was in charge of the arrangements.
The group arrived in the city on February 9. They had visited a few bars and had splintered, and the last place they were in was called the Hamborger Viermaster.
Eamonn told the programme: “We thought Liam had left just a couple of minutes before us.
“When he wasn’t waiting for us outside, there was no reason to panic.
“He’d organised the whole trip so he’d researched the city and knew better than any of us how to get home.”
When Eamonn woke the next morning, his brother was not there.
He added: “That’s when panic set in. I was sharing a room with him.
“We looked in all the other rooms but there was no sign of him.”
After discovering Liam was missing, Eamonn - a policeman himself - contacted 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.
A Facebook group has also been set up called Help Find Liam Colgan, and a video plea was made by Dundee United captain Willo Flood.
Police in Hamburg said on Wednesday they still hope to find Liam alive.
However, Eamonn said until his family finds out what happened, the wedding will not be a priority.
He told Newsbeat: “The wedding is not even a thought to me or my fiancee.
“It won’t be going ahead without Liam.”