Scars will heal slowly over time so anything you use to treat them might appear to be working.  Of the suggestions on this page, all of them might work, but the only one I can back up is the rosehip oil.   There does seem to be some evidence that rosehip oil reduces the pigmentation and therefore the appearance of scars.   I don't have the original references to hand at the moment but you can pick them up from http://www.dweckdata.com/Lectures/ASCC_paper_2003.pdf if you are interested.

I have heard that onion extract acts as an anti-inflammatory and inhibit the over-production of collagen in a scar. Onion extract is an ingredient in Mederma gel. It may require consistent use over several months in order to produce any effect.