The boy was strolling alongside Carlisle Avenue in Balaclava about 3.45pm on Friday, February 4 when a person allegedly touched the boy's groin as they walked previous one another.
The person was strolling in the other way to the boy and allegedly leaned over to the touch the boy as they handed each other, police mentioned.
Police have launched photos and CCTV of the person believed to be concerned.
He was believed to be aged in his 40s or 50s and was carrying a white t-shirt, blue denims and a cross physique bag.
Anybody who recognises the person or with info is urged to contact Crime Stoppers on 1800 333 000 or submit a confidential crime report at www.crimestoppers.com.au.