Summarize:

It's possible that your brother just simply doesn't understand why privacy and personal space are a big deal. Begin by talking to him and explaining why it bothers you that he goes through your things. Ask your brother how he would feel if you were touching his personal belongings, rearranging them, and possibly breaking them. Chances are, if given a moment to think, your brother will recognize that he wouldn't like it if you were doing these things. This will encourage him to reevaluate his behavior. Tell your brother that when he gets older (like you!), he will want his own space. It's possible that he doesn't understand that it's not appropriate to go through someone else's things without asking first. Yes, sharing can be a great thing, but it has its time and place. If the problem continues, consider asking for a family meeting to discuss privacy and personal space. However, don't create a situation where your brother feels attacked. Instead of accusing your brother of invading your space, explain how you feel when your space is invaded. In other words, stress your feelings rather than his actions. If your brother still doesn't want to leave your stuff alone, you could decorate a container or box and give it to him. Tell him that this is a place where he can collect his favorite things. You can put one of your brother's prized possessions in the box to get him started, and help him find a special hiding place for the box. This way, you will be teaching him about privacy and personal belongings in a way he can better understand. If your brother constantly messes with one or two of your belongings, see if there is somewhere else you can put those items. You could keep them in your locker at school, at a friend's house, or in your parents' room. For instance, if your brother sneaks into your room to play with your guitar, ask your music teacher at school if you can store your guitar there. You could also ask your parents if you can keep the guitar in their room when you aren't using it. Your brother will be less likely to sneak into your parents' room. If your brother is constantly snooping in your room, and you've tried everything else, explain the extent of the situation to your parents. Ask them if they would allow you to lock your room when you are not home so that your brother doesn't go through your things or break any of your valuables. Your parents might be hesitant to allow you to lock your room, since you would be locking them out of your room as well as your brother. Be sure to say that you want them to have a key so that they can access your room if need be when you are not home. If you share your room with your brother, you obviously can't lock him out of your room, because it's his room, too! Instead of asking for a lock on your room, you could ask your parents for a lock box where you could store the important things that your brother keeps messing with. Again, emphasize that you would want your parents to have a key as well so that they know you aren't trying to keep secrets from them. If your brother steals your phone, laptop, or ipod, you can password protect these items so that he cannot use them. Also, be sure to secure your online accounts (such as gmail and facebook) by changing the password regularly. Maybe you have a shared, family computer instead of your own laptop. If your brother snoops through your emails or social media accounts, be sure that the passwords aren't saved on the computer and that you have to manually type in your password to access your accounts. If your brother reads your school work on your shared computer, consider saving your work on a flash drive or in a password protected cloud storage platform, such as Google Drive or Dropbox.
Help your brother understand. Take away the temptation if possible. Ask your parents for a lock. Put a password on electronic devices and online accounts.