I was also mugged in Forest Hill the week before Christmas. I was walking home from the train station (8.30pm on a Sunday night), up towards the Horniman Museum. A guy came up behind me and tried to take my bag.
I didn't let go, so I got pushed to the ground. Luckily a family who were passing in their car noticed the tussle and pulled over to help. They chased the guy down and he dropped my bag.
The police caught the kid in the area, he's 13 and well known for mugging. He used to live in Forest Hill but is in Lewisham now. Apparently he's in and out of custody every 48 hours or so; they never have enough evidence to convict him. The police are still investigating my case, I think they hope my bag will have DNA evidence to help the case.
I wouldn't fail to report something, the sooner these kids get caught the better!