Look, if this happened to me I would do several things. Do as much research as possible regarding the date, time, and location where the earbuds went missing and document it. Use the location tracking on the earbuds to identify their location and print out the information. You may be able to determine who lives in the house with Google.
Call the appropriate law enforcement agency where the earbuds were last known to be. You can determine what agency covers the area with this website:
https://ravs.dcfs.lacounty.gov/
You may get lucky and find an energetic cop who will do a door knock for you. Because the value is low, it is a misdemeanor. Cops will not be able to write a search warrant, so they will need to make a voluntary contact with the people at the residence.
If this does not work for you, go to the school where the game was played and demand to speak to the principal, vice principal, and/or coach of the respective team. Lay out the facts and present the info during the meeting, specifically providing the address of the potential subject (most likely a high school age juvenile). The school has a database with the listed students and will be able to identify the person. Of course, they will not share the information with you, but you can ask if they can contact the subject and move forward with any administrative actions from the school's toolbox.
This is not a perfect resolution, but it will give you and your son a little satisfaction in your attempt to hold the person responsible without putting either of you in danger.
Let me know if you need any further assistance.
Rock on, David