I assume you meant that a car he was driving rear-ended a car you were driving.
That's a question for your attorney. If you don't have one, you should strongly consider retaining one. If you insist on handling this on your own, you'll have to learn the rules of procedure. If you are ultimately unable to serve (not "sever") the defendant, you may need to apply to the court to allow you to serve by publication. However, before you get there, hiring a private process server is the first step since they almost always do the job better than the sheriff. You may also need to hire a private investigator to verify the defendant's residence and maybe find where he works. You can also ask his insurer to accept service on behalf of the insured.
While this is true (anyone is "free to sue" anyone for anything), doing so would be frivolous. The defendant's insurer is not a proper party, and any attempt to sue would be met with a motion to dismiss that would be quickly granted and could get the OP sanctioned for frivolously suing the insurer.