David Greenwood said fewer than 100 of the estimated 1,400 victims identified in the Jay Report have taken part in a raft of new enquiries.
He believes "radical change" is needed for more victims to come forward.
It is nearly a year since the report into the shocking scale of abuse in the South Yorkshire town was published.
Mr Greenwood, who works for 58 of the girls subjected to sexual abuse by gangs of men in Rotherham between 1997 and 2013, concedes that improvements have been made locally in the past 12 months.
Two of the agencies that bore the brunt of criticism in the aftermath of the publication, South Yorkshire Police and Rotherham Council, have made progress but a truly independent organisation is needed to gain the trust of some survivors, he said.
"Both agencies have improved in Rotherham in the last 12 months but survivors of exploitation will be unwilling to come forward to them unless radical changes are made.
"An agency independent from South Yorkshire Police and RMBC [Rotherham Council] is essential for the 1,400 young women who need help.
"I am aware of only around 50 to 60 girls having come forward. This means there are around 1,350 whose lives could be improved with specialist help," he added.
The report by Prof Alexis Jay, published on 26 August 2014, detailed how children as young as 11 were raped by multiple perpetrators, abducted, trafficked to other cities in England, beaten and intimidated.
It revealed "blatant" collective failures by the council's leadership, senior managers had "underplayed" the scale of the problem and South Yorkshire Police had failed to prioritise the issue.
Its findings provoked outrage and a wave of resignations followed in its wake, the most high profile of which was South Yorkshire's Police and Crime Commissioner, Shaun Wright, who had been in charge of children's services in the town during the period some of the abuse happened.
The council was later deemed "not fit for purpose" by government inspectors and its powers were handed over to government-appointed commissioners.
The police now have a dedicated team of more than 60 working on child sexual exploitation (CSE) and its joint operation with the council and the Crown Prosecution Service, Operation Clover, has brought some suspected perpetrators before the courts.
The police insist they are working hard to restore trust with those affected by CSE.
Rotherham's police commander, Ch Supt Jason Harwin, said: "Over the last 12 months, if nothing else, restoring confidence has been really, really important and we've still got a journey to go on.
"The key focus has been around the victims and survivors. We need to understand better what the issues are for them and we could have done better and what we need to do for the future."
Mr Harwin said he understands the public want to see perpetrators jailed and that his force has arrested 460 people for child abuse offences in the last 12 months - with 76 of these suspected of involvement in "grooming and facilitation".
And he said 22 people have been charged with CSE-related offences in Rotherham, and there are currently 46 live CSE investigations in the town.
But Mr Greenwood believes despite South Yorkshire Police's best efforts a new approach is needed to convince more victims to speak up.
"Only when large numbers of girls affected feel able to speak to the police and with confidence that they will be believed, protected and supported will we know more," he said.
"I have spoken with many girls who simply want nothing to do with the police at present and until the police put in place really good tailor-made support from specialist and dedicated officers they will not engage."
"I would like to see a truly independent agency offering survivors good quality support, protection, talking therapies, help with housing, childcare and education.
"We still have a long way to go."
A fraction of the hundreds of victims of child sexual exploitation in Rotherham have sought help, according to a lawyer for some of the survivors.