The teenager, who has been named locally as Liam, was believed to have been a pillion passenger on the moped.
Officers say a car collided with the moped in Rocky Lane, near Great Barr, just before 7.20pm on Monday.
Now tributes and flowers have been left at the scene of the incident – while more than £1,300 has been raised online.
Anyone with information about what happened should contact West Midlands Police on 101, quoting incident 3771 of March 22.
Alternatively, contact Crimestoppers anonymously on 0800 555111 or at crimestoppers-uk.org
To donate, visit https://www.gofundme.com/f/xhb7d-liams-funeral-fund