Pop star Aaron Carter's worried mother has asked US tabloid the National Enquirer to help her warn her estranged son against so-called friends who could ruin him.

Carter has refused to meet with or take calls from his mum JANE since he sacked her as his manager for allegedly stealing from him.

But Jane still cares and now she wants her teenage son to beware friends who are giving him terrible financial advice, and she has asked the publication to print an open letter to her son in the hope he'll see it and get in touch.

She writes, "Dearest Son, I have always been truthful with you and will continue to be so. Aaron, I know the private jet rides can be thrilling. What is not a thrill is the day you get the bill for them all when you turn 18.

"Everything that has been spent on your behalf until now will come out of your own future earnings - if you're not careful."

And she also uses the letter to blast her ex-husband BOB, Aaron's father, who is fighting for full custody of Aaron.

She adds, "Don't allow your father full custody."