Emphasis is placed on the valuation of plain vanilla option when the price process of underlying asset is described by the stochastic Verhulst-Gompertz Equation with network externality effects in a complete market.  
The method is based on the change of measure, Girsanov theorem and martingale valuation techinique.  
The application to an exchange option is made attempt and the valuation formula for this option like the Black-Scholes one is derived.  
A simple relationship similar to the put-call-parity between the exchange call option and the put option is provided.  
Our results will be useful to analyze and to hedge the price  evolution at a sudden rise or crash of stock and commodity markets.