The 20-year-old, who was believed to be pregnant, instead went to see Adam Taylor, the father of her two-year-old son.
Mr Taylor was the last-known person to see her alive.
Police, who strongly suspect Ms Munnings was murdered, on Friday launched a renewed call for information about the cold case.
A coroner in 2012 ruled Ms Munnings likely died on or about July 23, 2008, the day she went missing.
How or why she died, or whether anyone contributed to her death, could not be determined.
Tasmania Police commander Stuart Wilkinson said investigators continue to believe there are people in the community with information around the circumstances of Helen's death and the location of her remains.
"It may be the piece we need to arrest and prosecute the person or people responsible for Helen's suspected murder," Cmdr Wilkinson said.
Mr Taylor, who has denied any knowledge of Ms Munnings' fate, told the inquest the pair had driven around Burnie on the afternoon of July 23.
He said he dropped her off on a highway near an old pulp mill about 6pm before returning home to his partner.
Mr Taylor first slept with Ms Munnings when he was 30 and she was 16, with the relationship continuing mostly in secret after she turned 17.
The coroner found their relationship was, at times, "characterised by ill will" but there was no evidence to support a finding that Mr Taylor contributed to Ms Munnings' death.
Ms Munnings' had told family Mr Taylor was the father of her unborn child, something he denied.
He gave evidence at the inquest he did not support Ms Munnings continuing the pregnancy because another child would place additional demands on her.
Police conducted extensive searches for Ms Munnings after she went missing but failed to find any trace of her.
The coroner said there was no evidence to justify a finding she took her own life, but it remained a possible reason for her disappearance.
In 2019, police used a specialist dog to search a number of sites in the state's northwest for Ms Munnings' body.
A $500,000 reward remains on offer for information which leads to a conviction, and the investigation remains ongoing.
The coroner described Ms Munnings' son as the dominant factor in her life and all the evidence strongly attested to her love, devotion and affection for him.
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