(CNN) -- The biological mother of a missing 7-year-old Oregon boy has written an open letter to her son saying, "I am sorry that I was not there to protect you."
"I am so soooooo sorry that this has happened," Desiree Young wrote to Kyron Horman in a letter that was released Monday to NBC News.
"I will never be able to forgive myself for being so many hours away when you needed me the most. I pray that you come back to me because I am afraid that I can't live without you."
The letter comes more than two weeks after the boy disappeared on June 4.
The boy's stepmother, Terri Horman, said she last saw Kyron walking down the hallway towards his classroom at Skyline Elementary School, police said. Cell phone records indicate she may not have been at the school at that time, according to a report in People Magazine. Authorities refused to comment on the report.
In the emotional letter, Young speaks directly to her young son. "When you come home I will show you all of [the] things that everyone did for you, just to find you," she wrote.
"There are literally hundreds of thousands of people that don't know you and yet they pray for you every night. They know how much I miss you and need you and they just want to bring you home to me. There are so many wonderful people working on this case and they are going to find you soon.
"I would give anything to run my fingers through your short hair again. I miss having you to hug anytime I want. Night time is always hard for me. I miss you so much and want you back here so that I can protect you from all of the horrible things in this world. I just can't believe that you aren't still with us," she writes.
"Your life has been really great and I know that it is [not] done yet. A long time ago you saved my life and now I am going to do the same for you. Our lives will never be the same after this. I love you very much!"
Authorities have labeled the case a criminal investigation, On Friday, they released a flier seeking information on Kyron's stepmother. The flier includes pictures of Terri Horman and a form to be filled out and returned by anyone who was at the school the day Kyron vanished.
"At any time did you see Terri Horman at or near the school?" was among the questions in the form.
Capt. Jason Gates of the Multnomah County sheriff's department issued the following statement Friday on the decision to request information on Kyron's stepmother:
"Detectives work in this case is exhaustive and they, along with Kyron's family, are asking for the community's assistance regarding anyone who saw not only Kyron, but also who may have seen Terri Horman and/or the truck she was driving that morning. Terri is the last person known to have seen him before he disappeared."
In a brief phone interview with CNN, sheriff's spokeswoman Lt. Mary Lindstrand said the focus of the investigation is not on Terri Horman.
"We're looking for every bit of information that we can," Lindstrand said. "We are not in a position to name anybody a person of interest."
Kyron was wearing dark cargo pants and a black T-shirt with the "CSI" logo on it at the time of his disappearance. He is 3-foot-8, weighs 50 pounds and has brown hair and blue eyes.
Anyone with information is asked to call the Multnomah County Sheriff's Office.