According to the Daily Mirror, tablets used in NHS terminations can cost as little as 78p on illegal websites, and can kill if taken in the wrong dosage.
Far Eastern gangs are bringing the drugs into the UK to target girls too terrified to tell their parents they are pregnant, the newspaper said.
Ann Furedi, chief executive of the British Pregnancy Advisory Service, called online pills “the backstreet abortions of the 21st Century”.
She added: “One in three women will end a pregnancy in their lifetimes but abortion sadly remains a stigmatised area of women’s reproductive healthcare.
“It is extremely troubling if any woman with an unwanted pregnancy feels her only course of action is to buy this medication online.”
She urged worried girls to visit the organisation’s abortion clinics and sexual health centres for a confidential appointment instead of taking their health into their own hands.
The Medicines and Healthcare Products Regulatory Agency (MHRA) tried to disrupt the supply chain with a series of raids earlier this week.
Investigators had been sold a prescription drug meant to treat stomach acid and ulcers as a home abortion pill because it makes the womb lining haemorrhage.
The watchdog is battling to shut down thousands of illicit websites selling counterfeit and unlicensed medicines.
Sites offering products for cancer, diabetes, arthritis and hair loss were found alongside fake condoms and erectile dysfunction treatments.
More than 1,200 websites were shut down last year but many are springing up to take their place.
Alastair Jeffrey, the MHRA’s head of enforcement, said: “When you buy medicines from an unauthorised source you run a number of risks.
“At best you will lose your money, at worst you can damage your health.
“People should speak to their GP or pharmacist who can advise them on the best treatment for their condition.”