Murder.Com

A killer kidnaps a victim, imprisons them and then webcasts their murder onto the Internet. Sometimes the victim's fate is linked to number of hits the website receives: either the victim will be killed when a certain number of hits are achieved, or the more hits received, the faster they die.

Usually depends on the police being somehow incapable of finding out where the server is. Which is highly implausible considering the bandwidth requirements of broadcasting live video.

An example of New Media Are Evil. Compare Snuff Film.

Nothing to do with trying to kill anyone from 30 Rock.

As a Death Trope, Spoilers ahead may be unmarked. Beware.

Examples of Murder.Com include:

Anime and Manga

Zombie Loan
Detective Academy Q
Hellsing TV series "Innocent as a Human"
Wolf Guy Wolfen Crest includes an absolutely sickening variant later on. More of a Gangrape.com though.

Comic Books

A Judge Dredd story set during the "Democracy" arc had a perp kidnap a neighbour and broadcast himself to all of Mega-City One, inviting the viewers to phone in and decide which of two increasingly painful and gory torture methods should be applied, culminating in the viewers choosing how the guy should die. There was always the option to vote to free him, but naturally, nobody ever chose that option.
The first storyline in the 2011 relaunch of Green Arrow has Rush stream his gang hunting a captured Green Arrow live onto the internet.

Films

Feardotcom.com tied it into a ghost story.
Untraceable, including "the more people watch it, the faster people die" element.
- So naturally the FBI gave out the web address at a press conference. As well as the fact that, in the police headquarters, every single computer is also logged on to the site. Would it have killed them to confine it to a single screen?
My Little Eye, although here the subjects aren't kidnapped; they've been told they're on a reality internet show about living in isolation. In reality, they're in snuff.
The movie The Condemned broadcasts a Deadly Game over the internet.
The Anvilicious Sick Room in Cradle Of Fear, where the site's visitors can determine how victims die, for a fee, but are at risk of becoming victims themselves if they don't pay up...
Near the end of the Spike Lee film Bamboozled, Mantan, the popular (black) minstrel performer, gets shot to death by a group of black radicals. The radicals webcast the murder live.
Snuff-Movie is a 2005 gothic horror film by British director Bernard Rose. It stars Jeroen Krabbe as a horror film maker named Boris Arkadin, whose pregnant wife was brutally murdered by a Manson like gang of hippy psychopaths during the 1960s. Because of this he has become a recluse, until, several years later, he makes a come-back and invites some actors to a large mansion in the English countryside to 'audition' for his new film. But unknown to them they are being filmed by hidden cameras linked to a 'snuff' website.
In Virtuosity, Sid 2.0, a serial killer personalty construct originally in a virtual reality system has figured a way to escape into the real world, takes over a TV studio and announces "Death TV" where the viewers get to vote by telephone on which member(s) of the studio audience dies.
In Kick-Ass, Frank D'Amico plans to stream the execution of Kick-Ass and Big Daddy live on the internet.
Subverted in Death Race. The death race is mandatory, but users don't control the deaths. Also, the entire event is a pay-per-view tv show.

Literature

Literary example: the short story More Tomorrow by Michael Marshall Smith. An abusive boyfriend forces a woman to pose for erotic pictures which he posts online...then the story ends with the next picture being titled "pretty_amputee".
"Man vs Beast" by Robert Muchamore. An extremist animal rights group intends to kill a TV chef by making him drink a very dangerous cleaning liquid and then broadcasting that over the Internet for everyone to watch.
In The Subject Steve, there is a variant of this near the end. It is described as "a revolutionary media space that binds together the most innovative aspects of gaming, spectacle, democracy and commerce."
For a while it seemed that every second (young)adult horror in the library was one of these.

Live-Action TV

Homicide: Life on the Street "Homicide.com": Quite possibly the Trope Maker here.
- Millennium "The Mikado" came about a year before the "Homicide" episode. They may be sibling Trope Maker.
Without a Trace "Party Girl"
Criminal Minds "Revelations"
- Played with in that most of the viewers of these videos don't realize that they depict real murders; they take them to be some sort of viral marketing campaign, which aggravates the murderers, who intended the videos to strike fear into the hearts of "sinners".
  - Well, murderer. And it wasn't so much that he was aggravated as, rather, horrified, and actually terrified because he wanted the murders to stop, and knew they wouldn't because the "audience" was Completely Missing the Point.
- Also "P911", though the unsub wasn't necessarily intending to kill the boy.
- And "The Internet Is Forever".
Season 4 of 24 starts with terrorists advertising they will kill a senator they kidnapped, as a Evil Plan to overload the Internet with viewers which would cause the safety systems at nuclear power plants to crash.
Numb3rs "Killer Chat"
CSI "Grave Danger": Nick Stokes is buried alive and the killer establishes a webcam link between the coffin an CSI. However, whenever the webcam is activated, the ventilation keeping Nick alive turns off.
- Alarm Fuer Cobra 11 did its own version of the same plot: "Begraben" ("Buried")
- CSI New York features an aversion - sure, there's a scary serial killer, but his site's password protected, and you have to find out using real life evidence.
The Last Detective "Dangerous Liaisons" as part of a Roaring Rampage of Revenge for the murderer's sister being killed in a Snuff Film years before.
Law and Order: Criminal Intent "Weeping Willow" (although here the crime is kidnapping, not murder, and it's clearly based on Lonelygirl15.)
NCIS "Murder 2.0". Video footage of the victims is uploaded to a thinly-veiled Fictional Counterpart of YouTube, intercut music-video style with other clips which provide clues for the team to follow.
An episode of season 8 of Spooks had a group of eco-terrorists kidnap a load of high-powered buisness man and host a live trial on the internet whether the businesses were unethical. If the internet voted them guilty, their execution would be streamed live.
Tracker had an episode that involved a kidnapped girl in a tank of water that was slowly filling up. Possibly a subversion in that the kidnap turned out to be a setup by the girl to get money from her father.

Video Games

The Joker briefly thinks of doing this (or at least floats the idea around) in Batman: Arkham Asylum.
In Devil Survivor 2, Nicaea shows videos of death... BEFORE they happen. It's so you can prevent it.

Web Comics

Achewood had resident murderous psychopath Nice Pete take the concept one further by having the murder be tied to an automatic device controlled by web poll.

Real Life

"Save Toby" (http://www.savetoby.com/) inverted this trope.
Domus Mortem (supposedly viral marketing but most DEFINITELY fake), featuring a poll that was open for a month for people to decide whether a cat should live or not. The "live" footage was prerecorded footage on a loop and despite the overwhelming majority of votes in favor of saving the cat, the votes to the contrary were artificially inflated and they "killed" the cat anyways. And then the stream showed a woman tied up the chair...