Going to the police can't make him worse off than he is now. And your poor daughter. I don't know how old she is, but he took her laptop, she knows it, you know it, and you won't call him in on it because he probably already sold it. How can SHE live that way? Why should SHE be the one who has to move?
The cops may straighten him out. It's worth a try. Whatever you are doing for yous son is not working and the definition of insanity is doing the same thing over and over again and expecting different results. Right now your son is a drug using criminal and allowing him to get away with stealing from his own sister is NOT going to make him change. He obviously has no remorse. Sometimes we forget there are other loved ones who need protection from our other kids who are frankly dangerous.
When I found out my daughter was smoking pot and got it from an adult (she was fifteen) I called the cops on her and the offender, whom I got her to name. To me smoking pot is much less serious than stealing (that came later), but I wanted to do what I could to show my daughter the consequences of doing things that are illegal and, in her case, hanging with adults who prey on minor kids. She was on parole twice. Eventually she was told to leave. She quit drugs, bad behavior and her lifestyle. I have no idea why or if it works for everyone, but getting tough love worked well for her. Ten years later she is living a boring housewife life with her boyfriend of eleven years and her little girl who is seven months old and what a great mother she is! She went to college on her own dime too. She worked until the baby was born, then decided to stay home with her so that they could have all the time in the world to bond. She has a house with her SO, a small one, but they bought it with their own money. She even quit cigarettes. She now has her home a non-smoking area. This from a kid who once did everything and loved meth.
I use her as an example of one person who benefitted from tough love, but frankly I don't think our adult kids benefit when we go soft of them because we don't want to involve the police, who can actually make a difference. Think of your daughter and her missing laptop which probably went to your son's drug habit.
I hope you do something good for YOU and put a stop to this kid's stealing...call the cops. Then concentrate on your loved oens who are respectful and kind to you and enjoy your life. We can thrive even when our adult kids are messing up. We chose our life's path and they choose theirs and we can't change what another chooses. But we CAN decide that WE want to live in a safe environment where illegagl activity does not occur under your roof, your sanctuary. And we can decide to protect ourselves and our other loved ones from the dangerous person. So what if he may get into more trouble? He will anyway. He's just asking for the cops to nab him for stealing from a stranger and, trust me, the stranger will have no sympathy at all. Don't try to protect him because you can't.
Hugs for your hurting heart. Be strong and do what you feel is right for you and your daughter.