Youths seen riding a moped on Saturday were described as "acting suspiciously".
Police received reports of two young people using the moped on the Bristol to Bath cycle path in Staple Hill, at about 12.40pm on June 22.
A witness wrote on the Greater Fishponds News and Views Facebook group that the pair were wearing black balaclavas and grey tracksuits.
He described the one at the front as being around 14 to 16, and the one at the back as being about 10.
The witness said they were heading towards Mangotsfield, before stopping to pick up a third person just after Teewell Hill bridge, then riding back towards Fishponds.
An Avon and Somerset Constabulary spokesman said the reports of the youths "acting suspiciously" were passed onto officers in the area.
