Stewart, England's most-capped Test cricketer with 133 matches, said that Richard Bailey introduced himself as the author of @KPGenius account during the Test against South Africa at the Oval in 2012 and revealed Graeme Swann, Stuart Broad and Tim Bresnan had access to it.
Bailey, who has no official connection to England camp, is said to be a close friend of Broad.
"I'm not here to protect KP and I'm not here to nail any England players. But I stand by the account of my conversation with this fella at the Oval in 2012, which is in KP's book, and I'm not in the habit of making up stories like that," Stewart said.
"I had a conversation with then ECB managing director Hugh Morris during the Oval Test match and then with England coach Andy Flower at a later date. I left them to deal with it. I felt they deserved to be made aware of it," he was quoted as saying by the English media.
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Bailey insisted a few days back that the England players were not directly involved in the account. But, Stewart said Bailey told him a different story two years ago.
"The reason why I'm prepared to talk about this is because Bailey said he didn't say anything to me, therefore doubting my integrity and I won't have that," said Stewart.
The account was closed shortly afterwards, with Bailey apologising "to anyone I know involved with England Cricket who I may have put in an awkward or embarrassing position".
Swann, Broad and Bresnan had assured them at that time that they had no involvement in the account.
Pietersen was dropped from England team two years ago for exchanging derogatory texts about his captain Andrew Strauss with South African opponents, but it could be embarrassing for ECB if evidence emerged of a campaign to belittle KP from inside the England dressing room.