Yes toothpaste helps to lighten the scars. Apply toothpaste (not the gel) regularly on the affected area in the night before sleeping and wash it off on the morning.
Also aloe vera combined with vitamin E in equal proportions when applied on scars will help to lighten the scars.

For more home remedies for acne and scars you can also read this article –
http://www.home-remedies-for-you.com/askquestion/4082/natural-remedies-for-acne-scars-home-remedies-for-.html
http://www.home-remedies-for-you.com/remedy/Acne.html

I have answered a similar question on acne scars, refer –
http://www.home-remedies-for-you.com/askquestion/4060/natural-cures-for-acne-spots-what-do-you-do-when-y.html