In 1998, he founded what would become one of the Internet's first major theater portals for theater news, reviews and production listings online, AmericanTheaterWeb.com. It was a site that predated and inspired such sites as TheaterMania and BroadwayWorld.com.
The uniqueness of the site and its pioneering nature for the theater community attracted remarkable press coverage, including a feature in The New York Times.
Propst continued to run the site through 2009, even as he began to write reviews and features for print publications, including Backstage, The Village Voice, TimeOut NY, and The Sondheim Review. He and AmericanTheaterWeb also became affiliated with XM Satellite Radio's XM 28 On Broadway Channel, and for four years, he provided daily "Broadway and Beyond" reports and served as a deejay for the channel with programs airing Monday-Friday.
In 2009, he joined the staff of TheaterMania, writing news and reviews, and providing ongoing coverage of theater music available digitally and on disc. He also served as Senior Editor when the site launched its iPad magazine app in 2011, a position he retained until 2013.
In addition to his writing, Propst served for three consecutive years as a nominator for the Drama Desk Awards (2005-2007) and was secretary and judge for three years for The Village Voice's Obie Awards (2009-2011 ).
Propst is an alum of the Eugene O'Neill Theatre Center's National Critics Institute and has returned to the program to serve as a mentor to young critics since 2008.
In early 2013, Propst provided the liner notes for two-time Tony Award winner Patti LuPone's CD Far Away Places. He is also a contributor to Huffington Post, and serves as a writer for Sh-K-Boom/Ghostlight Records.
His first book, You Fascinate Me So: The Life and Times of Cy Coleman, was published in April 2015 by Applause Books. He is currently working on his second book, an examination of the careers of Betty Comden and Adolph Green, for Oxford University Press.
Propst has also returned to reviewing for AmericanTheaterWeb.com and for the 2015-2016 season, is once again a member of the Drama Desk Awards' Nomimnating Committee.