I spoke to my wife about this as tracking down the owners of ‘lost’ pensions is something her company does.
The Tracing Group is known to her firm, but not used by them. The key seems to be will they charge you. Her company tracks people down and re-unites them with their pension/money using funds from the actual pension provider so they do not take anything from the person at the end.
Every week they have suspicious people replying to their correspondence, it gets even more fraught when they ask to see original documents such as passports and driving licences. Despite this suspicion they reunite people with £100’s/£1,000s on a regular basis.