There are several possible matches mentioned by people on the NCMEC Facebook page:
https://www.facebook.com/notes/help-id-me/30-years-later-and-still-no-name/949309928430248
The Jackson County, NC UID was 15 to 20 years old when found in 1983. He was 71" tall (5'11") and weighed 171 pounds. Short light brown hair. Might have been in Florida, Illinois and Tennessee before arriving in North Carolina.
Bringing them over here as a place to start. I don't see any of them as likely matches.
John Degnan III, Broward County, Florida, 20 year old white male went missing in Nov. 1980. He was reported to be 5'7" tall and weighed 145 pounds. So height and weight are off.
https://www.findthemissing.org/en/cases/20826/6/
Randy Sellers, Kenton County, Kentucky, 17 year old white male went missing in August 1980. 5'7" and 149 lbs. (He could have grown a few inches and filled out in 3 years. However, he has a tattoo and surgical scars, which our UID did not.)
https://www.findthemissing.org/en/cases/1712/1/
Daniel Naylor Alameda County, California white male, who was was 14 years old when he went missing in October 1982. Height listed as 5'9" and weight at 140 lbs. At age 14 he would still be growing.
https://www.findthemissing.org/en/cases/4544/0/
Gregory Mitchell, Polk County, Florida, 16 year old white male went missing in November 1981. Height estimated at 5'10" to 6'0" and weight at 200 lbs.
https://www.findthemissing.org/en/cases/5650/0/ and more info here:
http://www.charleyproject.org/cases/m/mitchell_gregory.html
His photo shown was taken several years before he went missing. FOUL PLAY SUSPECTED
http://www.missingkids.com/poster/NCMC/1150937/1
John Gosch from Polk County, Iowa was only 12 years old when he went missing in Sept 1982. White male, 5'7" and 140 lbs. (Too young to be the IUD and has freckles.)
https://www.findthemissing.org/en/cases/6131/0/
Bryan Fisher, Erie County, Pennsylvania, 16 year old white male went missing in Feb 1982. About 5'9" tall and weighed 180 lbs. (He has a few tattoos, so unlikely a match.)
https://www.findthemissing.org/en/cases/6060/0/
Michael Askren, Los Angeles County, California, 17 year old white male missing since August 1981. Listed as 5'7" and 140 lbs. Foul play suspected and being handled by LE as a homicide.
https://www.findthemissing.org/en/cases/5807/0/
A few people mentioned John Allen Troha from Michigan, but he has been ruled out. Other rule outs are : Steve Arrowood from North Carolina and Clifton Leonard from Florida.