The Bible doesn't describe unbelievers as wolves. It describes false teachers and false prophets who come into the church to preach another Gospel as wolves.
Unbelievers are generally just called sinners, unless they're in the church, in which case they're called goats.
A wolf is one who maintains that they are a believer.. but are in reality one who seeks to destroy from within and are not of the church.
A lost sheep is a believer who is out of fellowship with God and the term also refers to one who was at one point counted as being a child of God and would have refered to the house of Israel where spoken by Christ.