The information was requested by newspaper The Times and shared with International Adviser.
In the FOI, the FCA confirmed that four firms and four individuals are currently under investigation in relation to pension products.
None were named.
The total value of pension funds transferred is estimated to be £258m ($336m, €300m).
Additionally, the unauthorised introducers under investigation dealt with approximately 6,000 consumers, according to information currently held by the FCA.
Unauthorised introducers are generally based in the UK and are often instrumental in encouraging and facilitating the transfer of pension funds.
They do not necessarily require FCA authorisation, provided they do not offer investment advice and only service to introduce prospective clients to an FCA-authorised adviser who can provide independent financial advice.
Those caught offering investment advice are in breach of the financial Services and Markets Act 2000 (FSMA).
But absent evidence of unauthorised introducers breaching the regulations means that FCA’s focus is likely to be on the regulated entities that have provided the advice and facilitated the transfer or switching of a pension.
The FCA confirmed it is investing a significant number of regulated firms in this respect.