What is the most likely reason for an increase in the price of a specific stock

The most likely reason for an increase in price of a specific stock would be that the specific stock of whatever it maybe is either because it is:

· selling quickly. (which in terms brings the prices and the demand for it to be higher)

or 

· it could be very deficient which means that the material has decreased and become more valuable and higher of price because of it's rarity.