Unless your lease gave you a lien on his property as collateral for unpaid rent and expenses, you must first sue the roommate, including eviction case, win a judgment in your favor, then have court documents to permit such lien on that property, which I think you will have a difficult time getting. If you evict the roommate and they leave the stuff behind, you need to follow Cal. Civil Code sec. 1980-1991 to dispose of the abandoned property. Roommates are a hassle.
Below are a couple of links. The first is to the Department of Consumer Affairs Handbook for Residential Tenants. The second link is to the NOLO Press which has lots of materials for doing it your self re landlords and legal guides. Also check the Avvo guides for landlord-tenant issues.