Market price is based upon supply and demand, period. Supply could also be considered "lack of supply". We have no way of knowing if the "lack of supply" at any given moment is caused by lost coins, investors who are holding for a higher price, or hoarders that will never sell. Frankly it doesn't matter. We live in the now. The now price is based upon the current supply and demand, regardless of why. It will always be that way.
Even if someone advertised that they lost a bunch of bitcoins, I would not expect the market to react strongly. How could it be proven that the coins are permanently lost? Talk about a pump in dump scheme. Just pretend to lose coins, then find them again when the price goes up. Financial markets don't work that way.