Transcript for 'Missing Richard Simmons' highlights fitness icon's mysterious whereabouts
??? Richard Simmons has been a hero to thousands of weight watchers across the world. Dedicating his life to helping people maintain a healthy diet and work-out plan. His devoted followers would love to thank him, but they can't. He reportedly hasn't been seen by even his closest friends for years. Here's ABC's Nick watt. ??? ??? Keep those legs going, come on! Reporter: Richard Simmons, evangelist, showman, guru, sweating to the oldies, for decades. Hold the stomach in. Reporter: His signature, short shorts, a tank top and a smile. He doled out love, and he doled out weight loss advice to everyone he met. I gotta lose some weight. Don't eat in the car, that's number one. Reporter: He embraced it. Always accessible, omnipresent. Then in early 2014, just months after that Thanksgiving appearance, Simmons suddenly vanished, retreating behind the walls of his west Hollywood home. Bereft fans asked why and conspiracies swirled. Let's discuss the two main theories at that time. Now, three years later, Simmons, still out of the spotlight, and his disappearance from public life is the subject of the number one iTunes podcast, "Missing Richard Simmons." Three years ago to the day, Richard Simmons stopped being Richard Simmons, and I want to find out why. I met him in 2012, I wanted to tell his story way before any of this happened. The fact that he disappeared like he did, just kind of made it more urgent. Reporter: A producer for "The Daily Show," one of many who got hooked on the work-outs, became friends with the fun-loving fitness fanatic. Super foul-mouthed and hilarious and rude in a really funny way. He tells amazing stories. He cries every class. Come on, this is for you! Reporter: He's looking for answers. After about a year, year and a half, I started talking to people. Nobody was just thinking, he's fine, he's just taking time off. Nobody thought that. Reporter: February 15th, 2014, Simmons didn't show up to teach his regular class, his students bewildered. It's 11:35, okay, now he's five minutes late. Then it got to like 12:05, and we were like, what is happening. Like, I don't know if Richard's coming. And then people started leaving and someone subbed for him. Reporter: November last year, his studio doors closed for good. He opened slimmons in 1974, and said he opened it because other gyms in Los Angeles didn't really want overweight people. For Simmons, all shapes and sizes, everyone welcome. Not only did he stop teaching, one day he stopped returning my e-mails, my phone calls. I thought, well, that stinks. That's a drag. Then I realized he wasn't calling anybody. Or e-mailing anybody. Reporter: David Garcia, who lost 160 pounds, sweating to the oldies, same deal. The last time I saw Richard was here in this building in early February 2014. It snowballed and people started speculating all over the place. Reporter: In a phone call to NBC last March, Simmons insisted he's fine. You haven't seen the last of me. I'll come back and I'll come back strong. It was unusual that it was only a phone call and not in person. Reporter: Today Simmons publicist of 27 years told us, we didn't cooperate Noor collaborate with this podcast. The truth is that Richard is fine and willingly enjoying his life outside the spotlight, while still working behind the scenes to help those millions who desperately need his love and assistance. These unfounded attempts to diminish the legacy of this true American treasure are simply shameful. Chris Connelly profiled Simmons in 2009, taking us inside his west Hollywood home where Simmons would personally call those across the country struggling to lose weight. This is Mary faith. She began at 375 pounds, and now at 169. Hey, it's Richard Simmons calling. How are you? Reporter: Sometimes he would do this dozens of times a day. Not trying to sell them anything, except the value of diet and exercise. How many times have I personally told you how terrific you are? I know. How many? How many! Millions. Reporter: Yes, we love him for his enthusiasm, his exercise videos, and over-the-top TV appearances. Here on CNN's American morning. I love Richard Simmons. Thank you. Reporter: But it's his genuine love, his hidden largees that make him a true legend. I don't have to work anymore. I don't have to make a phone call anymore. I don't have to do one more leg lift. This is my passion, and this is my mission. Reporter: But despite his extroverted public persona, his personal life has always been a little solitary. Do I get lonely sometimes? Sure, you're on the road, you're not home, my dogs and my housekeeper, I'm attached to them. They're my, my sturdiness in my life. Reporter: When was the last time you were in love? I don't think I'm in love with a person, as much as I'm in love with what I do. No one should feel sorry for Richard Simmons. Because I think I'm one of the most loved people in the whole world. Reporter: Yes, there's a lurid tabloid fascination, but also now a genuine concern. Dan with his chart-topping podcast says he just wants answers. He's an interesting, gentle guy. And I think that's part of why people like him. I think that's part of why people are worried about him now. Because you feel that sensitivity, and you sort of feel, he's got a vulnerability. Reporter: So far the podcast has explored the questions and conspiracies. I'm here to talk about dalmatians. This brings us to Richard's disappearance number two, the dog theory. Reporter: But found no evidence or answers. This isn't a witch-hunt. I just wish him well. I haven't talked to anybody who thinks Richard Simmons is fine. Reporter: I'm Nick watt for "Nightline" in Beverly hills. If you're a podcast fan, subscribe to our ABC podcast for "Nightline." You can find all of our on iTunes, the ABC news app, or at ABC news podcast.com. And next -- ???
This transcript has been automatically generated and may not be 100% accurate.