The dedicated bench is a tribute to Paige Chivers, of Longford Avenue in Bispham, who was only 15 years old when she went missing in August 2007.
Despite public appeals and a police investigation, the former Montgomery High School pupil was never found.
However, Robert Ewing, then aged 60, of Kincraig Place, Bispham, was convicted of her murder at Preston Crown Court in July 2015.
There are two benches in Bispham dedicated to Paige, one of which was was unveiled by family members in the village in September 2015 after an online fundraising campaign raised over £700 to pay for it.
There was anger this week after a plaque on one of those benches was removed, prompting concerns that yobs may have pulled it off.
On social media page Bispham Chat, one member posted: "They should be ashamed of themselves, that is disgusting."
Another said: "That's disgusting, I hope they have CCTV and catch them."
And one group member added: "I’d happily donate to have it replaced."
It was said that relatives of Paige would approach Blackpool Council about a possible replacement of the missing plaque.