Mo. Rev. Stat. § 525.010: Who may be summoned as garnishees.

All persons shall be subject to garnishment, on attachment or execution, who are named as garnishees in the writ, or have in their possession goods, moneys or effects of the defendant not actually seized by the officer, and all debtors of the defendant, and such others as the plaintiff or his attorney shall direct to be summoned as garnishees.