I Don't Know Where I Am. Please Help Me

Seagulls cawed as River became conscious. The warm grainy feeling against his back and bare arms made his eyebrows furrow. With his eyes still closed, he felt around wondering what it was. Fists clenched, he felt the substance slowly slip away from his grasp.
River rose, curious of his location. It was blatantly obvious that he was nowhere near his room; he feared the worst. Was he in a drunken state not long ago? Are his pants still around his waist?
His head was groggy and upon opening his eyes, he realised that he was isolated. The substance he'd felt was sand. There was no one around him; he was stranded on an island.
River quickly stood up. He looked around to realise that the seagulls he'd heard weren't anywhere to be seen. Was he purposely abducted and brought here? His eyes suddenly widened. He had no knowledge of where he was or how he got there, and for the first time in decades, River was terrified.
He began thinking up ways of possibly gaining contact with civilization. For the first time in forever, River thought. He'd never needed to. Things came easy for him. If he wanted something, he'd get it within minutes. Being the son of a billionaire sure helped with that. Boy was he foreign to everything life was currently throwing at him. What a hopeless blonde.
In the distance, a mechanic roaring sound could be heard. It wasn’t just from there, but also up above. River looked up to find what he thought was a very strange looking plane flying overhead. It wasn’t in the usual shape of a plane, nor colour. He knew since he owned three. It was brown and almost triangular in shape. He dismissed the abnormality, nonetheless.
“Hey!” he cried out while flailing his arms wildly, desperate to catch the pilot’s attention. Alas, he was unfortunate. It was then that he remembered all those terrible stranded-on-an-island movies that he’d watched. Each one had something in common, forming the letters S.O.S with rocks. It wouldn’t hurt to try, would it?
River wandered around aimlessly like a fool, hoping to run into some decent sized rocks he could use. He found one near the spot where he laid unconscious. He began examining it. Doing this, something happened that shocked him beyond extreme. The rock turned static for a good second. He stared at it with his green eyes wide and filled with curiosity.
He found an aberration; there was writing. Someone had been on this island before. It read, ‘I don’t know where I am. Please help me’. This should have made the young lad hopeful, to know that he wasn’t the first to be stranded here, but it didn’t. It made his heart palpitate at an inhumane speed.
It terrified him to find his name written on the rock. River Luther.
He began stumbling around with it in his hands. This wasn’t possible. He wasn’t insane. Or at least that’s what he tried to tell himself. Dizzy and sick to the stomach, River bawled. He’d had enough. He was scared and alone with nowhere to go.
“AGHH!” he screamed. Through his tears, he could see the ocean. Static. He threw the rock at it in frustration. Was he hallucinating? There wasn’t even a splash. River felt something heavy land on his head and everything turned black. He fell back as he lost hold of consciousness. He found comfort in the darkness. With his last seconds, he whispered, “I don’t know where I am. Please help me.”
Seagulls cawed as River became conscious…