An ex band mate of mine gave away/sold a guitar I left at his house. It is valued at over $700. Is there anything I can do? I have messages between us where he acknowledges his mistake.
Consider a small-claims case for "conversion" - a tort. This is sort of the civil equivalent of the crime of theft. Obtain the Nolo Press book "Everybody's Guide to Small Claims Court in California." Also try putting "tort" and "conversion" into a Google search as your search terms.