The girl was approached by the man in New Street, Quarry Bank, between 8.10am and 8.20am on Tuesday.
It is understood he grabbed her arm and pulled her.
A passer-by saw what happened and stopped the incident.
The suspect, who is described as mixed race, aged 20 to 30, with brown hair and of medium build, then ran off in the direction of Bower Lane.
Officers have stepped up patrols in the area and are carrying out CCTV enquiries to identify the man who helped the girl.
West Midlands Police is asking him to get in touch.
Anyone with information can also contact police via live chat at west-midlands.police.uk, quoting investigation number 20/358306/22.
Alternatively, contact Crimestoppers anonymously on 0800 555111 or at crimestoppers-uk.org