The teenager, from Birchwood in Warrington, Cheshire, was found by members of the public as she lay wounded on a path in Linear Park, Culcheth, at around 3.13pm on Saturday.
Two 15-year-olds, from the local area, remain in custody after being arrested on suspicion of murder, Cheshire Police said.
Brianna was a transgender girl but police said there is no evidence to suggest her murder was a hate crime.
Paying tribute to the teenager, her family said in a statement: “Brianna was a much-loved daughter, granddaughter, and baby sister.
“She was a larger-than-life character who would leave a lasting impression on all that met her. Brianna was beautiful, witty and hilarious. Brianna was strong, fearless and one of a kind.
“The loss of her young life has left a massive hole in our family, and we know that the teachers and her friends who were involved in her life will feel the same.
“We would like to thank everyone for their kind words and support during this extremely difficult time. We would like to thank the police for their support, and witnesses for helping with the investigation.
“The continuation of respect for privacy is greatly appreciated.”
At the scene on Monday, a number of police vans could be seen parked in the surrounding area, with a number of uniformed officers patrolling the park.
Police tape lined a number of footpaths, cordoning off a large section of the area to the public, and police dogs could also be seen at the scene.
Flowers were also being left nearby, with messages including “Fly high angel.”
The headteacher at Brianna’s school, Birchwood Community High School, said they were “truly devastated” by her death.
In a statement, Emma Mills said: “We are shocked and truly devastated to hear of the death of Brianna.
“This is understandably a very difficult and distressing time for…
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