The messages expressed shock and grief, of course, but more than anything deep love and respect for the 61-year-old who was regarded as much more than a teacher to the schoolgirls and boys at Corpus Christi Catholic College.
The teacher – who was only weeks from retirement - was stabbed to death at the school on Monday in front of her horrified class.
Mrs Maguire was working on her day off when she was attacked and, according to the Daily Mail, she begged students to flee the classroom rather than see the horrific attack on her by one of their fellow students.
One teenager said: "Mrs Maguire was screaming at the kids in the class telling them to get out because she didn't want them to see what was happening."
It is understood the boy, described as a loner, chased her from one room to another before she collapsed into the arms of another teacher.
The teenager then dropped the knife and fled the room, according to some witnesses, before being tackled by the school's assistant headteacher.
It was the first ever murder of a teacher by a pupil in a British classroom. Pupils who witnessed the attack are now receiving counselling support.
As police started to question a 15-year-old boy about the attack, generations of pupils, past and present, shared their experiences of the Spanish teacher who was such an inspiration over her 40 years in the classroom.
Some left hand-written messages; others posted tributes on Twitter and Facebook with the hashtag #Aforanni, as in 'A for Annie', pledging to get A grades in their forthcoming GCSEs in memory of their teacher.
The poignancy behind them brings into stark relief the scale of the loss of Miss Maguire.
They tell a story of a woman who wasn't just a person passing through their young lives, but someone who inspired and influenced them: a woman who may now be gone, but had never been forgotten, and never will be.
The Class of 1978 wrote: "The teacher who made me smile."
The Class of 2001 declared: "Why couldn't life deal you the same fairness you dealt us."
And the Class of 2012 added: "Hope you're leading the choir up in heaven."
There's no doubt that her inspiration will live on.
One pupil wrote: "She would be so proud if we all got A's [sic] in our Spanish exams!' wrote one pupil."
"Let's do it,'" added another.
A third, from a girl called Niamh, said: "Putting my all into my Spanish work now."
Among the sea of tributes outside the school was a photograph pinned to the railings of Mrs Maguire standing next to Lucy Potter, 21, whose note read: "You always believed in me and took the time and effort to make sure I achieved the best I could."
Lucy – from the Class of 2009 – now works in a care home and credits Mrs Maguire 'for turning my life around'.
She said: "I rebelled a bit. I didn't do my homework and got behind with my coursework. But Mrs Maguire would always take time to talk to you after the day was over.
"I would say to her 'I can't do it' but she would say 'You can do it and you will do it' and made you believe in yourself." Lucy ended up with nine GCSEs.
One card was from the Hurley family read: "I remember your 1st year at Corpus Christi and you said you wanted to 'make a difference'. You have made such a difference to countless students including me and my own children, God Bless."
In fact, Brendan Hurley, now 53, was a pupil on Mrs Maguire's first day as a teacher back in the 1970s and his daughter Victoria, 17, was her pupil in the final term as head of Year 11 last summer, when she stopped teaching full-time.
Mrs Maguire was planning to retire at the end of the current academic year.
Marina Sheehan was one of three generations of her family to be taught by Mrs Maguire. The 36-year-old, her father Thomas Aspinall, 66, two sisters and two teenage children all benefited from her guiding hand. Mrs Sheehan said her death was like 'losing a best friend or auntie'.
She added: "She was so special and words can't describe what she meant to our family and the whole community.
"It is due to her that me and my sisters stayed in school and sat our exams when times were hard. And she's the reason I sent my kids to the school.
"Her life was that school. She was dedicated to her pupils and would always say she was available anytime to help us. She cared and was passionate and nothing was ever too much trouble."
Both Leanne Parker, 34 and her son, Jack, 18, were taught by Mrs Maguire.
Leanne said: "She was a fantastic teacher. You could always hear her singing around the corridors. She was firm but fair. My son loved her. No one had a bad word to say about her. She was always trying to get the children involved in extra activities.
"She was supposed to have retired at Christmas but stayed on to help the kids through their GCSEs."
Becky Simmons, 19, shared fond memories of a 'long-running battle' she had waged with Mrs Maguire over her hair colour.
She recalled: "I started dyeing it from year 9 but it was only in year 11, when Mrs Maguire was my head of year, that I really started to get in trouble.
"I remember her publicly telling me off for coming in with a bright pink fringe and my hair bright purple at the back, and she had to put me in isolation for three days, but privately she told me 'don't tell anyone but I quite like it'. She was so lovely."
Other tributes included this from Mr and Mrs Rowland: "You taught my eight children and you spent many nights singing in my living room in the choir."
And this, very simply put, from Megan and Grace Scanlon: "RIP Miss Maguire. You were such a lovely lady."