The 25-year-old shop worker was walking on parkland on Nechells Parkway on the evening of January 20 when the gang struck.
The woman, identified only as Sam, was dragged to the floor from behind and was stamped and kicked. As she lay on the ground the thieves stole her handbag and ran off towards St Vincents Catholic Church.
Detectives have released footage of two people they would like to speak to in connection with the robbery.
DC Tom Oppenkowski, from Birmingham CID, said: “Sam had just stepped off a bus and had to walk past a group of laughing teenagers.
“She thought nothing of it and continued on her journey but it appears that a man and woman from the group followed her and attacked her.
“Before and after the attack the teenagers were laughing almost as if this was a sport for them. Sam needed hospital treatment for her injuries and is obviously still traumatised by her ordeal.”
Sam added: “ I have been left traumatised by this and I have had to have some time off work. I was on the way to my sister’s flat when this happened and I ran to her flat and first thing I did was call my fiancĂ© who rushed over to be with me.
“I am on the mend but obviously it was a scary ordeal and sometimes if I am walking down the street on my own I get a little bit panicky.
“ I am disgusted that anyone so young could do something like this and laugh about it as well. I would ask them to bring themselves forward to the police.”
The group were described as a mixture of men and women believed to be in their late teens. One man had a Rottweiler type dog with him.
Anyone with information should call West Midlands Police on 101 or anonymously by calling Crimestoppers the independent charity on 0800 555 111.