After the band broke up, he starred in the Broadway production of Hair and the Tony Award-winning Sticks and Bones.
After four years in New York, he moved back to California to star in the television film Sunshine (1973), and featuring the songs of John Denver.
Since then, DeYoung has appeared in more than 80 films and television series, including Harry and Tonto (1974), The Lindbergh Kidnapping Case (1976), Captains and the Kings (1976), The 3,000 Mile Chase (1977), Centennial (1978) as John Skimmerhorn, Blue Collar (1978) as an FBI agent, Shock Treatment (the 1981 sequel to The Rocky Horror Picture Show) in which he played twin characters who sang a duet with each other, Master of the Game (1984) as Brad Rogers, and Flight of the Navigator (1986) in which he played Bill, David's father.
Also in the 1980s, he made a guest appearance on Murder, She Wrote, like fellow Navigator actor Joey Cramer.
In the 2014 film Wild, he played Ed, a summer resident of the Kennedy Meadows Campground on the Pacific Crest Trail.