The current system of monitoring sex offenders in the community is "unacceptable", it has been claimed.
Martin Cusick has been missing for more than two years
Scottish Labour MSP Paul Martin and Maggie Mellon of Children 1st told BBC Radio Scotland that sex offenders were not effectively monitored.
They were speaking after Strathclyde Police said a convicted paedophile had been missing for more than two years.
Registered sex offender and former policeman Martin Cusick, 52, from Clarkston, disappeared in October 2005.
Details - including a picture - were only released on Monday.
Cusick was jailed for five years in 1996 for abusing three girls aged between six and 12.
He was legally required to notify police of a change of address.
Mr Martin, Scottish Labour spokesman on community safety, said: "I would argue that the current arrangements are certainly unacceptable.
"First of all we have to look at the risks, not just the past risk but the future risks, of these individuals and look at their profile to consider that.
"I'm afraid at the moment that's not being carried out as effectively as it should be.
"People seem to have this perception that with registered sex offenders there is in place a very careful system for monitoring them, that is in fact not the case."
Ms Mellon, director of children and family services at Children 1st, said risk assessments were not managed properly.
"We only catch and identify a small percentage of sex offenders but when we do we don't seem to be able to prevent them posing a continued risk to children," she said.
"The judge sentencing Cusick said it was a depraved act against children that had permanently damaged them.
"Yet, we can only imagine that he has had at least two years where he has not been under supervision, nobody has known where he is.
"This is what we've got to focus on, the fact that when we know who these people are we do not have sufficient rehabilitation in place, we don't have proper management in place and they just seem to be able to go missing again."
Strathclyde Police said procedures must be followed when an offender goes missing and all lines of inquiry must be explored.
Tory justice spokesman Bill Aitken MSP said the force had "serious questions to answer".
"The public should have been notified and this man's photograph and description placed on the appropriate website a considerable time ago," he said.
"This is not acceptable."
Police said Cusick was not considered an immediate risk.