The girl was reportedly attacked in Reading, just after 10pm on Saturday.
Thames Valley Police say the two men began talking to the teen and walked a short distance with her before launching their attack.
Police are looking to speak with three Good Samaritans who rushed to the victim’s aid.
They are looking for two young men they believe fought off the attackers, as well as a woman who helped the victim after the alleged assault.
Investigating officer, Detective Inspector Sukhveer Sokhi said: “I appreciate that this offence will cause concern in the local community.
“I can reassure local residents that Thames Valley Police is conducting a thorough investigation.
“I am appealing to three Good Samaritans who helped the victim after the offence to please come forward.
“Firstly, two males, possibly boys in their teens, who intervened and had an altercation with the offenders in Prince of Wales Avenue around 10.25pm.
“Shortly after this altercation happened, the victim then walked into Elm Park Road, where a black woman helped the victim.
“We are appealing to these three Good Samaritans to come forward, because what you saw and heard will help our investigation.
“If you are the Good Samaritans or know who they are, please contact the force. You can either visit a police station, contact us via our website or call 101, quoting investigation reference number 43250584676.
“We have officers and staff in the community conducting house to house and CCTV enquiries. Therefore, if you have any information or questions, please feel free to speak to us as we conduct enquiries in the area.”
