Gold's Gym Owner Rainer Schaller's Missing Plane Crashed

Rainer Schaller -- who owns Gold's Gym, among other brands -- is still missing after his plane disappeared off the coast of Costa Rica, and his gym's parent company says the plane crashed.

The RSG Group issued a statement Monday confirming Rainer, his family and two others were on board the plane when it crashed.

There is still no official word if Rainer died ... though there are reports two bodies were found, plus luggage and pieces of the twin-engine plane.

The airplane wreckage was found at sea, so the situation does not sound good.

As we reported ... Rainer's flight disappeared overnight Friday, with the plane vanishing off the coast of Costa Rica on a flight path from Mexico.

Rainer is the…