Stock prices are absolutely determined by investors. As in, that’s the only thing that matters. If more people are selling than buying, line go down. If more are buying than selling, line go up. That’s how it works.
You say “shareholders,” but that’s not accurate. the OP said “investors,” which can mean everything from long-term shareholders to day-traders throwing around options. The former doesn’t determine share prices, those who actively trade the stock do.