Based on some research I did:
Her sister is still active on her Facebook page for Tammy and she is still stating she is missing.
There is a Find a Grave entry for Tammy Lynn Leppert because she is a missing person who disappeared in 1983 at the age of 18. The entry would be for a memorial, not a burial site, as her remains have never been found. She is a missing person who is presumed dead, and Find a Grave is used to memorialize missing persons and those who have died.