Legal Question in Civil Litigation in Washington

That the debt is in writing means you have 6 years from the creation of the note or the last payment made on it to sue on the note. If you can not find your "friend" you can file suit and having done a diligent search to find a current address, you may move the court to allow alternative service (by publication) and then (probably) a default judgment when your "friend" does not answer the complaint. Judgments are good for 10 years from entry, and may be renewed for 10 more. Where you would file suit may depend upon how much money is involved, small claims, district court or superior court. Also you should expect that the default judgment may be set aside when the party finally does appear (motion to vacate), but that simply means that they can then defend on the debt as they could have when you filed suit and if you had them served personally.