Being the victim of theft is an awful experience. On top of having something literally taken away, a victim can often be left feeling traumatized. Typically, when a person is robbed, or discovers something has been stolen from them, contacting the police is the first step.
If you know the perpetrator, depending on the specific facts of the situation, you may not want to involve police. However, failing to involve the police will put you at a serious disadvantage when it comes to recovering your stolen money or property. Although you can pursue a civil action against the thief for the return of your property, a criminal action can be resolved much quicker, and net the same result at no expense to you.