A break-in does not necessarily imply that there was a theft. Perhaps somebody could break-in to your house but your dog frightens them off before they steal anything. Therefore, the break-in happened but there was no theft.

To answer you more directly with the sentence you provided: People who suffered a theft should take measures to avoid future break ins. I would say this: People who are victims of theft, should take more precautionary measures to avoid/prevent future break-ins.

You could say this, and it would make sense. There are a TON of ways to say this though: 1. Someone stole from me. 2. I/We was/were burglarized 3. My home was broken into. 4. A thief stole (item(s)) from my home 5. We were victims of home invasion. 6. My car was broken into. I guess what I am trying to say is, is that there is no "right" way to say this but a native speaker would probably describe the incident a little more clearly with something like the examples I provided. Good question!

A break in is a burgalry, this is specifically a theft from a house. I would put it in present perfect. I would also use a hyphen for 'break in' as it's being used as a noun if I'm not mistaken. People who have suffered a burgalry should take measures to avoid future break-ins.