Ms Mitchell went missing on the 2 June, before a man was then charged with her murder just over a week later.
The North Down MLA said: “To hear of yet another instance in Northern Ireland where a young woman’s life has been so cruelly taken from her, before it even really had the chance to begin, is absolutely devastating.
“My thoughts and sympathies are with Chloe’s family, friends, and loved ones at what must be an unimaginably difficult time. Whilst no family should ever have to go what they’re going through, the strength and resilience they’ve shown has been incredible.
“Standing in the crowd at the vigil for Chloe in her home town, the profound sense of loss within the community was palpable. It’s abundantly clear just how many lives she touched, and just how missed she will be.
“Gender-based violence is a scourge on our society that has taken the lives of entirely too many of our women and girls, laid claim to too many of their futures, and we all have our part to play as a society in not only tackling it, but getting rid of it for good.”