Is it permissible, in Sharia, for shareholders to demand the actual value of their shares, and is the CEO's action of acquiring company assets without their knowledge considered theft, and what are their legitimate rights in this situation?

Most contemporary opinions permit the establishment of joint-stock companies if their activities are lawful, and there is no objection to making decisions in them by a majority of the partners. The CEO in these companies is an agent of the shareholders and is bound by their decisions; if he violates them, he is liable for damages. What the CEO did by purchasing your shares without your knowledge is impermissible for two reasons:

1. The agent's action is restricted by the limits of the agency. If he violates them, his action is not effective. The CEO's purchase is void according to the Shafi'is, and contingent upon your approval according to the majority of scholars.

2. It is not permissible for an agent in a sale to sell to himself. This is the view of the Shafi'is and Hanbalis, and one opinion within the Hanafi school.

Therefore, you have the right not to approve what the CEO did, and the shares remain your property. You also have the right to sell them for a price you deem satisfactory. The CEO is liable for damages for any company funds he took for his own benefit, and his action is considered a breach of trust.