The 16-year-old was stabbed on a bus in Hagley Road on Thursday, while on her way to school in Halesowen.
A 22-year-old man arrested on suspicion of fatally stabbing Christina has been sectioned under the Mental Health Act.
The Reverend Mike Rutter, whose church is near Christina's school, said people were thinking of her and her family.
St Peter's Church in Lapal has opened a book of condolence and Mr Rutter has held prayers remembering the girl, who attended nearby Leasowes High School.
Similar prayers were said at the Birmingham Christian Centre, close to the family home, where the Reverend Mark Ryan urged the community to stick together.
Mr Rutter said: "Most people are thinking about Christina's family and her friends and thinking about the school and how the school are dealing with this.
"The people I've spoken to are really just expressing shock.
"I would invite anyone who feels that they need the space to come along to St Peter's but I'd also invite people to think where it might be more appropriate, by the school or on the number 9 bus route, but we're certainly a place for people to come."
More floral tributes have been left near the scene in Hagley Road over the weekend as friends continue to pay their respects.
A post mortem examination revealed Christina died from a single stab wound to the chest.
West Midlands Police said the 22-year-old suspect was not previously known to mental health units in the area and had no known link to the teenager.
He was assessed by mental health professionals on Friday who deemed him unfit to be interviewed any further by detectives.
The fatal stabbing of schoolgirl Christina Edkins on a bus in Birmingham has left the community in shock, a vicar has said.