Question : Before I started practicing Islam and I didn't care about permissible and prohibited things. I used to work for my father and while I was working I unlawfully took some money from his company. Do I have to admit this to him?
I took out a loan for my father and he was supposed to pay it back in a year but he couldn't. So if I agree to make the repayments every month instead of him paying it can I repay him in this way without telling him that I took money from him all those years ago? Or should I tell him?

Answer : You should pay back what you have taken from him but it is not a must to tell him what you have done in the past. The monthly payment can be considered part of your repayment to him if you are not contributing but you are paying on his behalf.
Question : When I was in school I went to a supermarket with my friends and I stole a magazine, this again was before I was practicing Islam. Now the supermarket isn't there and there is a new one. So, my question is how should I atone for this? Should I give money to charity on their behalf?
Answer : You should look for the shop owner and pay him/her the said amount and you do not need to inform the owner why you are paying when you find him/her. If you could not reach him/her, it is enough to be prepared to pay the owner his/her dues when possible.
Paying the amount as a charity on behalf of the owner when he/she can not be reached is a good thing but it is not mandatory and does not remove the obligation on you to satisfy the owner whenever you can reach him/her.
Question : If a person has stolen something and he cannot find the owner? Is it then sufficient if he pays the value in Sadaqa? What if it is a big company or something alike and it is hard to find out how he should pay it back?
Answer : Yes, it can be paid as a charity on behalf of the item’s owner but it is not obligatory if the owner was unknown. It is enough to intend to give it back when the owner is found although, it is better to pay it as a charity on the owner’s behalf.
If stealing was from a big company, then the owner(s) are known. He should turn the item or its value to the manager or deposit the amount in the company's bank account where the owner(s) can access it.