The fact that the ninety and nine were following the shepherd assured their salvation. They were justified because they stayed under the watchful care of the shepherd and they trusted in Him.
They were justified by the actions of the shepherd. For we are justified by faith through grace and not of works lest any man should boast.
The lost sheep is only lost because he has failed to do one thing, follow the shepherd. He may now be lost, alone and scared but he does not know how to get back with the fold.
The shepherd left his throne in heaven to find the lost sheep of the house of Israel.
If you are lost and don't know Jesus, simply ask Him to find you and make you his own.
One way the Shepherd can find a lost sheep is by that sheep crying out. The Word of God states, "Whosoever shall call upon the name of the Lord Jesus shall be saved. Cry out to him from your lost place and I guarantee you He Will Find YOU and bring you Safely Home!!!!