Psychologist Laura Richards, who ran the Homicide Prevention Unit, said stop and search is no better than a "sticking plaster", and feared the policy could "further alienate marginalized young men" and drive them into the arms of gangs.
"We are seeing that a number of guys committing murders are already excluded. I fear we just make the problem worse," The Telegraph quoted her, as saying.
Richards warning came as popular rapper Dizzee Rascals called for an end to the UK's knife crime epidemic.
The rapper, who was born and brought up in London, is encouraging teenagers to ditch knives.
"The world is a big place and the more bulls**t you do, the more time you are wasting. Think about life a bit more and know there is more out there for you. It's all there if you want it," Rascals was quoted, as saying.
Scotland Yard, however, insists that stop and search is a key part of its overall anti-knife crime strategy, saying that it sends out a "visible message" to young people that its aim is to keep them safe.
Figures show officers carried out 48,869 stop and searches in the capital in May, June and July, taking 1,445 knives off the streets. There have been 21 deaths of Brit teenagers due to knife crimes in 2008 so far.