My friend is bullied by 6 people. What do I do?

My new friend of this school year (call her Sm) and I have gotten really close. She's really sweet and tells me a lot of things but today she told me that everyday, after school when she walks to the school behind ours, to pick up her little sister, 6 9th graders will follow her and push her around until sm arrives at her sister's school. I have looked through the yearbook with her and she can't find them. They weren't at school today so she couldn't point them out to me. This has been going on for a month and I want to help Sm but I can't find those boys in the yearbook. Help me! She wants to tell the school staff once we identify them but I find it really hard to keep it in! My sister knew many people at my junior high (because she graduated there) but she can't seem to find anything either. Sorry if this is long but I'm just really concerned. Sm has been bullied a lot in elementary for speaking out about bullies (they called her a snitch all year) and she's scared something like that will happen again :( please help

UPDATE:
My friend was walking again yesterday and she was pretty sure they weren't at school. On the fence their was a bag of candy and a not that said "Dear ____, we're sorry." We hope they are sincere but we haven't seen them at school today either. Sm wants to confront them the next time she sees them.