Replevin is a court action to recover the possession of personal property. It allows a person to request an order for the immediate delivery of their property after a hearing. Personal property is any property that is not land or buildings.
Washington LawHelp has information about the replevin process as well as sample demand letters.
The basic state laws for replevin are found in RCW 7.64.
The Clark County Sheriff's Office has a list of their requirements for replevin.
Self-help kit from the law library
The law library sells a Replevin in Superior Court self-help kit that includes forms and instructions to ask for an order requiring a person or business to return a specific piece of your personal property valued at $300 or more (for example, this can be a vehicle or a pet or anything except land or a building). Kits can be purchased at the library or online and mailed out.