The PPF covers employer schemes, not personal.
Personal pension schemes run under a trust deed (i.e. Stakeholders from life companies) are covered up to 90% of the value should the business fail. Note, this is not protecting you against investment losses.
Trust-based schemes have more limited cover - up to the first £50,000 only. Both type sod cover are provided by the FSCS.
The FSCS also provide cover in the event of the individual investment providers failing, up to £50,000, or £85,000 for cash deposits (per banking institution). Again provided by the FSCS, neither offers protection against normal investment loss.
Unregulated investments are not protected however, compensation may sometimes be sought through other routes, notably who sold you the investment.