Change in times do not necessitate the coming of a new prophet. 
It is true that times have changed. The previous age was a traditional one, while now we are in a scientific age. Earlier people lived in a pre-civilization age, but today we are in a post-civilization age. This is a clear fact. The coming of a new prophet is not necessary for changed times, rather changes in age require the performance of ijtihad (re-interpretation and re-application of religious teachings). In this new situation, we are required to do ijtihad. A new prophet need not take birth. 
Why does a prophet come to people?
A prophet comes to teach people basic principles. He does not provide details. The task of ijtihad begins during the very lifetime of a prophet. There is a famous incident according to which the Prophet Muhammad sent some of his Companions toward the encampment of Banu Qurayzah. When the Companions were leaving Madinah, the Prophet advised them:
That is, "Offer namaz only after you have reached the village of Banu Qurayzah." So, clearly the Prophet gave the above instruction to his Companions with extra emphasis. When the Companions had reached close to the village of Qurayzah, the sun was about to set. Some of the Companions were of the opinion that the Prophet had clearly told them to offer Asr namaz only after reaching the village of Qurayzah, and not on their way. But another group of Companions did ijtihad. This ijtihad comes in the category of one that was done during the very lifetime of the Prophet. Some Companions took the Prophet's words literally, saying they would offer namaz only after they have reached the village of Qurayzah. But another group of Companions took the advice of the Prophet in the sense of moving swiftly or with speed. They clarified that the Prophet really meant that they should not delay their journey. This is an example of ijtihad by the Companions of the Prophet. Ijtihad had started during the very lifetime of the Prophet, then how can we say that the exercise of ijtihad should be stopped now? Another unwise step taken by people was that they closed the doors to ijtihad. In truth, ijtihad is an act which is forever intrinsically connected to human life. If the doors to ijtihad are closed, people will ask for a new prophet. If the doors to ijtihad are closed, this is the situation we will have to face. 
According to me, change in times do not require a new prophet, rather they require us to perform ijtihad. Changes in age do not require a new prophet, rather they signal the need to perform ijtihad. Moreover, ijtihad is a task which must continue in every time and age. 

In today's times we are in need of ijtihad. We are in need of a person who understands both the religion of Islam and the times in which we live today. He must be aware of both the traditional [religion] and the modern [age]. He must provide guidance to people according to the requirements of the present age. We do not need a new prophet. We are in need of a religious scholar who can perform ijtihad. We do not need anything else.