Merseyside Police have called on South Yorkshire Police to issue his picture in an attempt to track him down.
Detective Chief Inspector Mark Drew, said: "On the 22 February a 21-year-old woman was subjected to an appalling series of assaults which resulted in extensive injuries.
"This abhorrent behaviour and abuse is totally unacceptable and I would urge Lewis Dunn, who could have information which would assist our inquiry, or anyone who knows where he is to come forward."
He added: "No-one should have to tolerate being treated this way regardless of their gender or sexual orientation. Making those first steps and reporting abuse can be daunting and there are many reasons why people find it hard to do, but there is support available, not just from the police, but other organisations too.
“Domestic abuse is a priority for the force and our work remains firmly focussed on investigating this abhorrent crime, supporting survivors and bringing offenders to justice. I want people to be confident of the measures we have in place to support them and their families with our whole partnership response.
"The force has invested in a number of specialist resources it can call upon to investigate domestic abuse and support the victims of this heinous, under-reported and often hidden crime. We are committed to ensuring women are protected and their needs are put first in these situations.
"Throughout the last year we have worked hard with partners to protect and support women and girls who are faced with violence and sexual abuse.
“We know the strength of working together in partnership when it comes to tackling domestic abuse. We already meet on a regular basis with our strategic partners and review demand for services to ensure that victims are supported and able to access vital services. Together we are actively addressing the fears being raised about violence against women, with the ultimate aim of making our streets safer for women and girls."
Anyone who knows the whereabouts of Dunn is asked to get in touch via @MerPolCC on Twitter, or anonymously to Crimestoppers on 0800 555 111, quoting 0438 of 24 February.