Did not sign lease renewal but named on current lease--am I still liable?

My question involves landlord-tenant law in the State of: California

I was in a 12 month lease with 2 other roommates for August 2008-August 2009. We had a 4th roommate after the contract started but I am not sure she was ever officially added onto our lease, even though the leasing office accepted rent checks from her. My original roommates decided to sign the lease renewal for the next 12 month period at around March 2009 around and only informed me after the fact. At the time, I was not sure whether I wanted to continue living in the unit for the next leasing period, so I never signed the lease renewal. However, I paid my share for the entirety of the original 12 month lease that I have signed.

I am a college student scheduled to study abroad during the spring so I only needed housing for a semester. Out of convenience and consideration for my two original roommates I decided not to move out when the old lease ended and opted to stay in the unit for part of the duration of the renewed lease since they had difficulties finding replacement roommates. Later on we had a new 4th roommate move in who definitely isn't, as of now, on the 2009-2010 lease. Relations between my roommates and myself have never been great due and I moved out after the semester this month, just like I have informed them I would earlier. Now they are harassing me and forcing me to pay for rent while I am away and have already vacated the premises.

I called the leasing office about the status of current lease and their representative has said that I, along with the two original roommates, are named for the 2009-2010 lease. I have never seen a copy of this lease (I had no reason to ask for it before) and as I've mentioned before, I have never signed the lease renewal. Can my roommates or the apartment management hold me liable for part of the rent of for the rest of this lease if I am somehow named on it (probably because it is a renewal of the previous lease which I did sign) but I have never signed it?

Unless your original lease said it automatically renewed at it's expiration, you are not obligated for the renewal term. Your signature is not on the renewal. You stayed on as a m2m tenant after the lease ended. Remind the leasing office that you did not sign the renewal and your signature does not appear on it. You are a month to month tenant with no lease. Let the roommates know the same thing. Give both a written 30 day notice that you are vacating if you have not already done so. Pay for that 30 day period and no more.

You should have received a copy of your lease. It is usually required by law that the landlord provided one anyway, regardless of whether the tenant "needs" it or not. It is always in the tenant's best legal interest to make sure they receive a copy. It's odd a tenant wouldn't even want a copy of their lease. It's a legal document.

You are a month to month as of now, and you can move out without further penalty as long as you give a 30 day notice to the landlord.

Never NOT receive a copy of your lease. In the future, make sure you ask for it.