The warning was issued as a couple from the Democratic Republic of Congo were found guilty of murdering the woman's 15-year-old brother during an "exorcism ceremony".
The Metropolitan Police yesterday said it had investigated 83 "faith-based" child abuse cases involving witchcraft in the past 10 years but believed it was still an "under-reported, hidden crime".
Children's charities and campaigners urged communities to report abuse and said social workers must be firmer in confronting abuse in immigrant groups.
Kristy Bamu, 15, was relentlessly tortured and eventually drowned in a bath on Christmas Day 2010 by his sister, Magalie, and her partner, Eric Bikubi. The killers are facing life sentences.
They believed he had cast spells on another child and punished him with increasing viciousness. The teenager "begged to die" because he was in such pain after three days of being attacked with knives, sticks, metal bars and a hammer and chisel, suffering 130 separate injuries.
Among the cases that have come to light are four murders, including that of Victoria Climbié in 2000, the case that first raised awareness of the problem in Britain.
Detectives warned that while they were investigating around eight cases a year, they believed many more incidents went unreported.
Det Supt Terry Sharpe, the Metropolitan Police's lead on Project Violet, a team set up to tackle religious-based child abuse, said: "The intelligence from the community is that it's far more prevalent than the reports we are getting."
The NSPCC said: "We must not be afraid to challenge these communities to out the wrongdoers within them. Sadly, this deeply disturbing case is not a one-off incident. "
The Victoria Climbié Trust, which was set up after the death of the eight year-old, said that, while the number of children affected was relatively low, the impact was significant. "The reality is that no one really knows the full extent across the many communities for whom traditional belief systems are the norm," said director Mor Dioum.
The charity Trust for London said some officials may be unsure how to deal with abuse cases linked to witchcraft and spirit possession.
"Those working with children need to remember that no faith or culture promotes cruelty to children and not be afraid to intervene if someone is wrongly using belief as an excuse to harm children."
Many cases involve immigrants from African countries such as the DRC, where witchcraft is widely practised, and are nurtured by an increasing number of African churches.
Kristy had come to London with his two brothers and two sisters from Paris to stay with their sister and her boyfriend for Christmas, but within hours Bikubi, 28, had accused them of bringing kindoki - a form of witchcraft - into his home.
Two sisters, aged 20 and 11, were beaten but escaped further attacks after "confessing" to being witches.
Kristy was singled out because, in sheer terror, he wet himself. He was struck in the mouth with a hammer, had bottles and tiles smashed over his head and his ear twisted with pliers.
In what prosecutors called "a staggering act of depravity and cruelty", the siblings, who included a 13-year-old boy and an autistic brother aged 22, were made to join in the torture.
At one point, Bikubi, 28, a football coach from Newham, east London, told the youngsters to jump out of the window to see if they could fly.
One of the victims, Kelly Bamu, said: "They started talking about kindoki, witchcraft and this and that. It was as if they were obsessed by witchcraft."
The Old Bailey heard that emergency services were greeted with a horrific scene when they were called to the eight-floor flat following Kristy's death. In the blood-spattered flat, police found his brothers and sisters "hysterical, terrified and soaking wet," the court heard.
Bikubi and Bamu, 29, who had denied murder, will be sentenced on Monday.