PLOT: internet killer

I was browsing through fiction prompts and saw the heading: Once Upon a Tweet. It consisted of an author who told a story through prose bursts a tweet at a time. This got me to thinking... tweeting can be so anonymous. And so many people communicate this way nowadays. Either through tweeting, or Facebook, Tumblr, pinterest... the internet is so mainstream that everyone is connected somehow. What if.... a serial killer were to use something like Tweets, or YouTube videos as a way to broadcast his kidnapping/killings. I wonder how long it would take for someone to catch on to a random "I'm going to kill today" Tweet. And then maybe followed with. "I found my victim. Her name is ___. I picked her up in the parking lot of a grocery store." How long would it actually take for someone to realize that this was not a joke and indeed something real. I was thinking the killer could maybe even post a video on "YouTube", or something similar of course, and maybe even found his victims by perusing the "facebook" style sites. Call him the Internet Killer or something catchy.

The MC could either be his next target or involved with the investigation. I don't think I could write a good cop character as I have no idea what goes on in that lifestyle. But someone who had to have short interactions I could probably handle. Maybe the MC has been getting visions and she helps the police out. Or, maybe they believe she's the next target, etc. Help me out here guys if you have any thoughts, I'd appreciate it!!