Roommate disappeared with some of my things

My recent roommate (he moved in two weeks ago) disappeared last night with all of his things as well as many of my personal belongings. He didn't take anything of significant value, just food, kitchen items, lamps, and shelves, but my main concern is that he still has my key!! My other concern is that when I got home from work last night, my front door was unlocked and ajar. Luckily, my dog stayed in the house, because I would have been heart-broken if I had lost him. I have to admit- I don't know for sure that my roommate took the missing items, because anyone could have walked in with door open. I'm not sure what to do at this point. I'm not home for a majority of the day, and I have to get approval from my landlord before changing the locks. So far, I have not received return phone calls from either my landlord about the locks, or my roommate. Any ideas??

If you don't hear back from your landlord within a reasonable time, and the issue is simply swapping a doorknob, you may wish to "take a chance" by changing the doorknob yourself (giving a key to your landlord). If your landlord objects, put the original doorknob back on.