Detective Chief Inspector Chris Jones from the Metropolitan Police said that the force was offering a £20,000 reward for information leading to a conviction.
"Whilst two years have past since the murder of Samuel Guidera, the MPS remains committed to identifying and bringing to justice those responsible. I am convinced there are persons within the community who for reasons, be it family or other loyalties, have yet to come forward with the information they have.
"I would ask them to consider the devastating impact Samuel's death continues to have on his family and loved ones and appeal for them to contact the investigation team. The MPS continues to offer a £20,000 reward and I would stress any person coming forward will be spoken to in confidence with all measures to protect their identity and safety considered."
More top news
Man who has barricaded himself in house for three days may have a stash of petrol and other explosives, police say.
Transport secretary Chris Grayling said MPs will decide this week about where to allow airport expansion in south east England
The Met Police has thanked residents in Northolt for their patience but has warned the armed stand-off could take time to resolve.