How can we find missing beneficiaries (life insurance and defined benefit pension)for whom we do not have social security numbers? (This is not a terminating plan.)

What is our obligation to do so? If we have made a reasonable effort,(And what constitutes a reasonable effort? Do we need to hire a locator firm? Can they locate
someone without a social security number?) what then? Do we turn the money (in the case of pension) over to the PBGC? (Or does that just apply to terminating DB plans?) Will the PBGC try to locate them?