Caoimhin Cassidy Crossan, 18, was found dead in a stolen car in Galliagh in June. The car had gone on fire after crashing into a lamp-post.
At the time, police said he was not travelling alone and there were reports of two men leaving the scene.
Det Insp Michael Winters said those men need to come forward.
“Think about Caoihmn’s family, his family are still coping with this every day and I think they will continue to cope with this for the rest of their lives,” he said.
“Put yourselves in their position, think about how it effects them and give them the truth.”
A post-mortem examination later revealed he had not been seriously injured in the crash, but died after the car caught fire.
The body of the 18-year-old from Creggan was found in the car on Fairview Road on Saturday 1 June.
The car was stolen from a house in Oakfield Crescent earlier that day.