Richard Simmons' fans won't let it go ... they're convinced he's in peril -- so much so, they're calling police to check on him.
Hours before Simmons did a phone interview with NBC ... we've learned one of his fans was on the horn to LAPD. Our law enforcement sources tell us the anonymous person called a tip line to say Richard was being held against his will.
We're told police will NOT be conducting a welfare check on Simmons for a couple of reasons: first, as we've reported ... LAPD checked on Richard about a year ago. They spoke to him face-to-face and found he was "fine." Secondly, police heard him on "Today" reiterating what he already told them.
Bottom line -- cops are convinced Richard's not being abused or held hostage.