We have to check everyone's bag to know the thief.

To motivate our class friends how much important the money is.

We will complain to our respective class teacher and principal.
If u have any kind of theft in your class its really a matter of concern. Immediate steps can be taken ie. as soon as you find a theft you can contact your teacher and in absence of students you can search their bags and I really feel that this matter shall not be conveyed to other teachers or even to principal because there is a possibility of spreading of rumours about your class..