Stopping a shoplifter-Preventing monetary damage

Preventing monetary damage from occurring to a friend:[1]

If one is able to save his friend from a possible monetary loss, he is obligated to exert as much effort possible, with all his bodily strength, to try to prevent the loss.[2] Doing so is a positive command and is included in the Mitzvah of Hashavas Aveida.[3]

Example-Prevent flooding:[4] One who sees [a stream of] water threatening to flood the field of his friend, or to destroy his home/building, is obligated to build a fence in front of the water [to block it] on their behalf [if the friend is not around and is thus unable to do anything to prevent the damage].

A gentile:[5] One is not required to help prevent damage from occurring to the property of a gentile, unless there will be a Chilul Hashem involved in not doing so.

Summary:

If one is able to save his friend from a possible monetary loss, he is obligated to exert as much effort possible, with all his bodily strength, to try to prevent the loss. He however is not obligated to spend money in order to help prevent the monetary loss unless he is certain that his friend will reimburse him for his expenses. One is not required to help prevent damage from occurring to the property of a gentile or a Mumar Lehachis and Apikores.

Q&A

If one saw a person shoplifting in a Jewish owned store, must he inform the owners?

Yes, as stated above! This applies even if the shoplifter is a Jew and is of young age and may be arrested for his actions.