Paris Mulholland wrote the letter to the thieves to let them know how she felt after they raided her Doncaster home and stole her presents.
In the letter Paris wrote: “To my burgler [sic]. I hope you are happy with yourself, I can no longer sleep in my own bed and guess what, [for a few] years I have had a fear of the dark and before you burgled me I had accomplished my fear - but once you stepped in my room my fear had started again.
“Why could you not have left when you saw to [sic] picture of a happy family and when you saw my birthday card, but anyway thank you for scaring me so much I cry 2 hours straight nearly every night.”
Thieves broke into the house on Thursday, a week after her 11th birthday.
Mum Gemma Mulholland said the letter had helped her daughter tell the thieves “how she feels, and how it’s affected her.”
She said: “I really am super proud of her.”
Paris’ new iPhone, a laptop she got for Christmas, and birthday money was taken from her bedroom, as well as her grandmother’s gold watch.
Cash, jewellery and other items were taken in the robbery, along with Paris’ and her younger brother Thomas’ belongings.
Ms Mulholland said Paris was too upset to sleep in her bedroom after seeing it ransacked.
Lego models were broken and photos taken on Paris’ phone during a recent trip to Disneyland may have been lost forever.
Ms Mulholland called the thieves “despicable human beings” but said the community had rallied round.
Anyone with information should contact police on 101.