There is no lease with landlord only a verbal agreement that each person would pay their part of rent directly to the landlord. Upon going to pay rent for December I informed the landlord that I will be moving from the house on Jan 1, 2013. When arriving back home my roommate was moving out and refused to pay her part of rent. She did not inform the lardlord about moving out, didn't give 30days notice and didn't pay their agreed upon part of rent. So does the landlord have the right to hold me accountable for the non paid part of rent? Or did the landlord forfeit that right upon accepting my part of rent & my 30day notice and had a verbal agreement with all tenants that they were responsible for their own part of rent?

If you had all been on one written lease, the landlord could hold any one of you liable for the entire rent for all of you. But without a lease, and accepting rents from each of you, he cannot.

This could go either way in court. Generally a landlord rents a unit in entirety. Without a lease making each rommate individually responsible, the norm would be to make each roommate wholly responsible and require you to sue the roommate for their share. The fact that landlord accepted rents directly might mitigate that in court.