The incident happened in Royal Road between 7pm and 7.15pm on Monday, June 26.
The offender began talking to her before he sexually assaulted her and cycled off towards Hatfield Road.
Shortly afterwards, the same offender approached the victim again in Brampton Road where he spoke to her and sexually assaulted her again.
The victim, who was physically unharmed, then ran to a nearby house to seek help.
Officers investigating a sexual assault in St Albans have released a facial reconstruction of a man they would like to identify as part of their enquiries.
Detective Constable James Kier, from the Local Crime Unit, said: “This was an understandably distressing incident for the victim and she is being supported by our officers while the investigation continues. I would ask that anyone who recognises the man pictured to please come forward and speak to us. I would also like to reassure the community that this is an isolated incident and we are doing all we can to trace the offender.”
If you recognise the man pictured, please contact Hertfordshire Constabulary via the non-emergency number 101, quoting crime reference F1/17/3027 or report information online at www.contacthertspolice.uk/Report/Crime.