Watkins, 36, of Pontypridd, changed his plea as his trial was due to start at Cardiff Crown Court alongside two women on Tuesday.
South Wales Police say they are looking into issues raised by a dozen calls.
The police chief who led the inquiry said officers would "work tirelessly to identify any other victims".
Watkins will be sentenced on 18 December.
A force spokesperson said: "Since Tuesday the incident room has received around a dozen calls from the public and we are looking into any issues which have been raised."
Watkins admitted two counts of attempted rape and 12 other offences including sexual assault and taking, making and distributing indecent images of children.
The court was told the two women who stood alongside Watkins in the dock sexually abused their own children and made them available to Watkins for him to abuse.
Woman A admitted the attempted rape of a baby after denying rape and two charges of sexual assault, as well as taking and distributing an indecent photograph of a child.
Woman B pleaded guilty to conspiring to rape a child, three sexual assault charges and four charges of taking, possessing or distributing indecent images.
The evidence against Watkins came from computers, laptops and mobile phones with some recovered from "cloud" storage.
The court heard that he had filmed and kept the episodes of abuse which took place in various hotels in London and south Wales.
Det Ch Insp Peter Doyle described it as "the most shocking case I have ever seen".
After Tuesday's hearing, he told reporters: "The outcome does not mark the end of our investigations and we will work tirelessly to identify any other victims or witnesses and seek the justice they deserve."
South Wales Police worked with other forces, Interpol, National Crime Agency's Child Exploitation and Online Protection Centre (CEOP) command, local authorities in England and Wales, the Department of Homeland Security in the USA, and the NSPCC.
Police are investigating new leads following a public appeal after Lostprophets rock singer Ian Watkins admitted child sex offences.