Tenn. Code Ann. § 8-8-220

In any civil action when the service of process is attempted to be served and is subsequently returned unserved, the sheriff of any county may appoint a person, who is a citizen of this state and who is of legal age, to serve such service of process within the prescribed limitations on service of process. Such appointment shall be made in writing and shall be filed with the court in such civil action. A person appointed to serve process as provided above shall be paid the appropriate fees, make an appropriate bond, assume such liability as the law requires, and file an affidavit with the court in such civil action indicating service of process was served, as is provided for appointments made under § 8-8-108.