The victim was going to collect her bicycle after visiting an Asda store in Barrhead, East Renfrewshire, when she was attacked.
The man, who wore a white trilby-style hat, struck outside the town’s Main Street Shopping Centre at about 8.15pm on Sunday.
Detective Inspector Gillian Patrick, from Police Scotland, said: “This was a particularly traumatic experience for the young girl concerned, who had been out in the local area before being attacked.
“I would like to reassure the local community that we are continuing extensive enquiries into this incident.
“We know the man was in the shop prior to the incident taking place and I am appealing to anyone who may have been shopping around that time to think about whether they may have seen this man or noticed anything suspicious.
“If you have any information or knowledge about this crime, please talk to officers and pass it on - it could prove vital in helping us trace the man responsible for this attack.”
The suspect is described as 20 to 30 and of medium build. He wore a grey zip top with white striped sleeves, grey jogging bottoms and grey trainers. He was carrying a black holdall.
Ms Patrick said: “I’m aware this incident will be of concern to people and I would like to confirm that additional patrols will be in the area to offer reassurance to local people and if anyone has any concerns, please speak to officers.”