21-year-old Kavan Brissett was fatally stabbed in an alleyway off Langsett Walk, Upperthorpe, on Tuesday, August 14.
His younger brother, Kerthanie Brissett, says the red Honda Wave 110iÂ scooter bought for him byÂ Kavan was stolen from a property in Stannington between 10pm and 11.30pm last night.
Kerthanie, aged 20,Â said: '[The scooter has] sentimental value as my brother, Kavan,Â bought me this scooter. It's the last thing he bought for me.
'And now it's gone from low people.'Â He added: 'Whoever finds my scooter or knows anything, I'll pay them cash.'
Anyone with information should call South Yorkshire Police on 101, quoting incident number:Â 14/131953/18.Â
After being stabbed once through the chest, Kavan was rushed to hospital. He had emergency surgery, but died four days later.Â
An 18-year-old man arrested on suspicion of attempted murder and three boys -Â two aged 17 and one aged 16 -Â arrested on suspicion of conspiracy to rob, have all been bailed pending further enquiries.
Earlier this week, detectives confirmedÂ 29-year-old AhmedÂ Farrah, who is also known as Reggie, was wanted by South Yorkshire Police becauseÂ they believe heÂ could hold vital information about the fatal stabbing.
They claimÂ he knows he is '˜wanted' and that he is actively evading arrest.
Jude Ashmore, of South Yorkshire Police, said: 'Efforts to find and arrest Farrah, who is known to frequent the Broomhall area of Sheffield, have been ongoing but so far we haven't been able to locate him.
'I'd also like to remind anyone who is letting Farrah stay with them, or helping him to evade arrest by any means, that you are committing a criminal offence which could result in prosecution.
'Farrah knows he is wanted and is deliberately avoiding police and I'd ask anyone who has any information, and Farrah himself, to think about Kavan's family and the pain they are suffering. Do the right thing and contact police."
Anyone who spots Farrah should call 999.
Those with information on where he might be should call South Yorkshire Police on 101 and quote incident 827 ofÂ August 14.
The police incident room can be called direct onÂ 01709 443507 or information can be passed to Crimestoppers, anonymously, on 0800 555111.Â Â