Officers want to identify a teenage boy as they’d like to speak to him in connection with the offence.
They also want to identify two potential witnesses who were in the area around the time the incident happened as they may have information which could assist the inquiry.
Detective Constable Toby Hayes said: “This was a truly awful offence on an innocent young girl.
“She was out socialising in Bristol city centre last summer when she met a boy who separated her from her friends and attacked her in an alleyway.
“We’ve worked tirelessly to investigate this incident but regrettably we are yet to identify the offender.
“Due to nature of the offence and the ages of those involved we’ve been keen to protect them from this incident being reported in the media and talked about online however we have now reached a point in our inquiry where we need the public’s help.
“We’re releasing an image of a young man dressed all in black who we hope the public might be able to tell us who he is.
“We’re also asking for the public’s help to identify an adult and a young child in other images we’re releasing as we think they may have witnessed part of the incident.
“We appreciate the images aren’t the best quality but we still hope someone might recognise those in them and help us obtain justice for the victim.”
DC Hayes added: “We’ve been keeping the victim and her family updated throughout our investigation and have provided her with access to specialist support.
“What she went through was horrendous and I’d like to praise her for the bravery and courage she continues to show while we try to catch her attacker.”
If you can help, please call 101 and give the call handler the reference number 5221144902.
You can contact the independent charity Crimestoppers anonymously on 0800 555 111
