THE mother of 15-year-old Martha Fernback, who died after collapsing at Hinksey Park in Oxford, said the hundreds of tributes to her daughter was giving her a lot of comfort.

Police and paramedics were called to the park off Lake Street, South Oxford, about 1.15pm yesterday after she suffered a cardiac arrest.

She was airlifted to the John Radcliffe Hospital where she later died.

Her mother, Anne-Marie Cockburn, wrote on a Facebook tribute to Martha: "Thanks so much to all Martha's friends, I am finding so much comfort in reading your lovely messages about my girl. We all loved her so so much."

More than 1,300 people have liked the page.

Martha's family have also released a formal statement through the police. It said: "Our beautiful girl was taken away from us yesterday, she was the most extraordinary, effervescent human being and all her family and friends felt so privileged to have known her.

 "We are all utterly devastated and have sought such comfort in the beautiful condolences we have received from everyone."

The family has released a photo of Martha, with her pet rabbit Bluebell.

Thames Valley Police said the teenager thought she had taken the substance MDMA, widely known as the drug Ecstasy.

The force is continuing to investigate the death of Martha, from Oxford, and today floral tributes have been placed in the park opposite South Oxford Community Centre.

Friends have been gathering close to Hinksey Lake, opposite the community centre, to lay flowers in her memory, and people have posted tributes online on social networking websites.

Senior Investigating Officer Det Insp Brendan Murray said: "Firstly our thoughts are very much with Martha’s family, who have been left devastated and distraught by her death.

"Following our initial enquiries we now understand Martha had taken a substance earlier that day which she believed was MDMA.

"It would be wrong to speculate on what this substance was or what caused her death, as the investigation is still at an early stage.

"A full post-mortem examination will be carried out tomorrow, which will include toxicology tests.

"It is likely to be several weeks before the results of these tests are known.

"I would strongly urge young people not to take or experiment with illegal drugs such as MDMA.

"They are extremely dangerous and often contain poisons and illicit chemicals which can prove fatal."

If you have information which could assist the police inquiry, please call CID in Oxford on the 24-hour police enquiry line on 101 or the Crimestoppers hotline on an anonymous 0800 555111.

Police are publicising FRANK, a confidential drugs advice helpline for young people, which can be reached by calling 0800 776600 or by visiting:

A 17-year-old boy from the Oxford area has been arrested on suspicion of possession with intent to supply a controlled drug, in connection with the ongoing investigation, and he is currently in custody for questioning.