Emcee

Emcee Duties Without Shadowcast

The emcee might be an usher or theater management (or possibly radio personality if their station is sponsoring the show) who just welcomes the audience, explains any theater rules regarding prop bags, thanks any movie sponsors, then asks the audience to enjoy the movie (might include having audience spell R-O-C-K-Y ("give me an R", etc) or chant "lips, lips, lips" to cue projectionist).

Emcee Duties With Shadowcast

"The Emcee of the show should explain the theater's rules loudly and clearly during the pre-show... The pre-show should be coordinated by the President, but should be run the Emcee, which should be the same person every week. In your pre-show you should always mention the names of the performers for that night, as well as information about how to reach your cast online, the RHPS Official Fan Club, and info about how to become a part of your cast.

http://www.rockyhorror.com/participation/transuniv.php

Emcee Duties With Shadowcast And Preshow

An example is shadowcast's The Denton High Drama Club Policies and Procedures emcee duty list...

Pre-preshow Announcements (raffle tickets, prop bags, Facebook page, how to join cast and crew, etc)
Welcome
Reading Of The Rules
Conduct Costume Contest
Call for Virgins, audience may chant back, “Whatcha going to do to the virgins?" to which the MC may reply, “We’re going to pop some cherries tonight!”
Virgin Pledge
Host Virgin Games
Introduce Any Live Acts
Post-Preshow Announcements (raffle tickets, prop bags, Facebook page, how to join cast and crew, etc)
Drawing (raffle tickets)
Cue Projectionist (have audience spell R-O-C-K-Y ("give me an R", etc) or chant "lips, lips, lips")
Introduce Shadowcast (at end of movie with movie cast credit pictures)
Closer (meet in lobby for photos, thank you for coming, we are the (blank) shadowcast)

Sal Piro

One famous Rocky Horror Picture Show emcee is Sal Piro, "Sal Piro is the president of The Rocky Horror Picture Show Fan Club, a position he has held since 1977. Piro was a part of the original Waverly Theatre audience, from which the unique audience participation elements and much of the film's cult following were born. This following has gone on to become a worldwide phenomenon." - Wikipedia

A brief example is available at this video link RHPS Say It! 1975 Audience Participation Audio only on youtube. The video automatically starts playing 45 seconds into the video so reset video to very beginning to catch emcee by Rocky Horror Legend Sal Piro also a Rockypedia link here.