And I'm livid... to have waited on the phone for 15 minutes to be told that "we can't find your bag, so gather up your receipts for your items in the bag and we'll reimburse you."
How about "NO." Just find and send me my bag, it's not that hard.

Story is, I flown overseas from Asia on Cathay Pacific airlines to LA airport, and had a connecting flight to florida. When I landed at LA to claim my bags to recheck them, one of my bag was gone... after waiting for over an hour. I spoke to airline representative by the Cathay Pacific airline carousel at the time, and he reinsured that he'll meet me in an hour to let me know the updates... he never showed up.
I flew back home in hopes that someone might have picked my bag up and rechecked it instead of taking it home, but I ended the night in disappointment and at the JetBlue baggage claim office. The JetBlue representative told me that I'll get a $30 voucher for my inconveniences, and it'll be delivered to my house when found.
Fast forward a week and a half later... No sign of my bag. I just called JetBlue and the incompetent manager of my claim case was unable to coherently tell me any information about my bag, other than "we'll still look for it."

I'm at my wits end and without my valuables for almost two weeks now and I'm not sure what happened to it.
Only explanation is that someone must have taken my large suitcase...
Or it's still sitting in LA airport somewhere.

But I hope it's the latter, or just got transferred to another destination.
Should I also call and contact Cathay Pacific or just leave it to JetBlue? I was told that the last airline is responsible for lost/damaged bags. But it's been so long, even if found, my bag must be in the dump by now.

EDIT: Case in point that she was "incompetent", calling me back 5 whole hours later, claiming she got my email wrong. I then had to stay on the phone with her (I requested so) to MAKE SURE she was able to send an email right this time... Oh, it only took 6 minutes for her to send the same email. No biggie, she just suck at her job.