Josh Hanson, pictured below, from Kingsbury, died on Sunday, 11 October 2015, after suffering a serious wound to his neck. Police were called out to the RE Bar in Field End Road, Eastcote after reports of a stabbing.
The reward money is available for information leading to the arrest and prosecution of Shane O'Brien, 28, who has links to the Ruislip area. See picture below.
He is now thought to be in Dubai, according to the Metropolitan Police Service.
Officers said they urgently want to speak to Mr O'Brien about the “unprovoked and violent murder”, adding he has become of Britain's most wanted fugitives.
In March, Mr O'Brien was added to the most wanted list by Crimestoppers and the National Crime Agency. At that time it was believed he could be hiding in the Netherlands.
However, latest information suggests he has travelled to Dubai, police said today.
The murder investigation has gained nationwide coverage, having been featured on the BBC Crimewatch show late last year.
A police statement read: “O'Brien, originally from Ladbroke Grove, is described as white, 6ft with grey eyes and short dark brown hair. He may use the name Troy O'Brien.
“He should not be approached by members of the public. Any sightings of him should be reported to police immediately on 999.”
Detective Chief Inspector Noel McHugh, from the Met's Homicide and Major Crime Command, said: "We hope the offer of this substantial reward will encourage anyone with information to come forward and help us detain O'Brien.
"Clearly O'Brien is being helped by other people to evade police - some of those allegedly assisting him have already been arrested. The fact that O'Brien is moving from country to country demonstrates he has the means to travel without using his own identity.
“So we would ask people to look closely at O'Brien's photo and if you recognise him contact us. He has a distinctive tattoo on his back that says 'Shannon 15-04-06' which may help identify him.
"While our information links O'Brien to Dubai, we have taken calls about potential sightings across the world which have all been followed up.
“We really need the public's help - please share O'Brien's 'wanted poster' both online and in premises and if you have information don't assume it's something we already know, you could hold that crucial clue."
Josh's mum Tracey Hanson said: "It has been eight-and-a-half months since my son and Brooke's brother Josh was murdered in an unprovoked knife attack and we are still fighting for justice.
“Not a single second, minute or hour of the day goes by without us not being able to properly grieve or mourn for Josh as Shane O Brien, the man police would like to speak to in connection with Josh's murder, is still at large.
"We are asking the public to help in any way they can, if you have the slightest doubt in your mind as to whether you think you may have seen Shane O' Brien or know someone who has, please come forward and help us get justice.
"Our lives will never ever be the same without Josh and it just gets harder and harder every day, so please if you have any information at all no matter how small or irrelevant you think it may be, please call the police."
DCI McHugh added: "Josh was a hard-working young lad, up at 5am for his job as a roads planner and often working seven days a week. He had everything to live for and when he went out that Saturday night, no one could have imagined what would happen to him.”
Two men have been arrested as part of the investigation.
On Wednesday, 28 October 2015, detectives arrested a 24-year-old man and a 29-year-old man - who were on an inbound flight to the UK - on suspicion of perverting the course of justice and assisting an offender.
Both remain on police bail pending further enquiries - next due on a date in early September.