All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
The evidence that it is a recommended act for the preacher in the Friday speech to supplicate is that Imaam Muslim reported that Hussayn Ibn 'Abdur-Rahmaan As-Sulami narrated: "I was sitting next to 'Imaarah Ibn Ru'aybah As-Sulami and Bishr Ibn Marwaan was delivering a Friday speech and when he supplicated he raised his hands. Thereupon 'Imaarah said: "May Allaah disgrace these hands. I saw the Prophet when he was delivering a Friday speech, and when he supplicated he pointed up with his index finger only." So, 'Imaarah denied raising the hands but confirmed supplicating during the Friday speech. This is evidence that the Prophet used to supplicate when delivering the Friday speech but he did not raise his hands. As regards the congregation, some scholars are of the view that they should not raise their hands when saying 'Amen' as there is no evidence on this, and the Prophet prayed many Friday prayers with the companions and were they used to raise their hands when he used to supplicate, this would certainly have been reported to us.
As regards saying Amen, it should not be said loudly. The Maaliki and Hanbali schools are of the view that saying Amen should be said silently. Whereas, the Shaafi'ee school is of the view that Amen should be said softly without raising the voice, and the Hanafi school is of the view that one should say 'Amen' in his heart only.
To conclude, all of the four schools agree on saying Amen but they differed with regard to the method of saying it. This difference of opinion is very old and each group gives its own evidence. Therefore, it is not possible to solve this difference of opinion once and for all, and a person should not waste his time arguing about this, and it should not be a reason for dispute or causing an affliction among the Muslims.
Allaah Knows best.