I didn't see this girl, on the ruled out list, the pic isn't too great but she had been missing for 7 years prior to JD being found, plus Cynthia was already 5'4" at 13 years old!!!..... Just another possibility!
http://www.doenetwork.org/cases/858dfmi.html
Cynthia Coon
Missing since January 19, 1970 from Ann Arbor, Washtenaw County, Michigan.
Classification: Endangered Missing
Vital Statistics
Date Of Birth: March 24, 1956
Age at Time of Disappearance: 13 years old
Height and Weight at Time of Disappearance: 5'4" (162 cm.); 110 lbs. (50 kg.)
Distinguishing Characteristics: White female. Brown hair; brown eyes.
Dentals: She had straight teeth, no fillings, never been to a dentist.
Circumstances of Disappearance
Cynthia Coon left her residence en route to school in Ann Arbor. She did not attend school at all that day and did not return home that evening.
She made contact with her family twice, once on April 1, 1970 and again on April 2, 1970. She did not know her whereabouts at the time of the calls. An extortion-type call was received by the family on May 5, 1970. Since that time, no further contact has been made with the family.