congratulations on finding the dude.
If actions taken by the police stalls which it probably would. I recommend calling one of those car accident lawyers you see on TV unless you know a decent lawyer yourself already.
I personally would not have approached him without legal counsel. he now knows its you and your after him so he has time to change\twist his story. And maybe even report the accident to police thus potentially minimizing any decent sentence from a judge.
Your lawyer can send a legal letter to him[s] threatening[/s] "advising" that if he doesn't accept full responsibility and agree to pay all damages to your insurer and legal costs you will take him to the magistrates court so the judge can decide.
You have said that he is 17 and has no insurance. It is easy to therefor speculate he wont have the money upfront to settle out of court.
Congratulations! now its time to find some nice clothes and tell your employer you will need to have some time off work soon as your going to court. (if you decide to not take a lawyer you will still have to represent yourself and be willing to assist police in court because its your word against his)
SA Police will also be present to account for all actions police have taken (you logging a report, him not logging one, etc
If he actually did do it AND failed to report the accident even after you approached him he is fairly boned. he would need a good lawyer and a fairly lenient judge to wriggle out of not loosing his license.
Start writing everything down. dates\times of contact etc. if you haven't already.
Some further reading below.
http://www.police.sa.gov.au/sapol/road_ ... _crash.jsp