Not necessarily ... the sold shares would just fall into the inventory pool of shares for the Market Maker firm that executed the transaction.
Typically, when anyone sells shares, the shares are just added back into the overall inventory of shares available. When anyone buys shares, it is generally the same case.
If the pool grows bigger, the price drops in response to "clear" inventory. If the pool grows smaller, the price increases ... etc.
In addition, that inventory pool of shares is used by Market Makers to hedge against option risks (i.e. sold calls, sold puts, etc) and shorted positions.
The goal of these market makers is to stay neutral on all transactions will pocketing the difference in the spread. There is ALWAYS a pool of shares.
My understanding of this could be off, but this was what was taught to me by a friend of mine who worked for a Market maker firm several years back.
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