The artworks, paid for by the community in Stirchley, were covered in thick silver paint sometime during Friday night.
Peter Evans, of the Friends of Stirchley Park, said it must have taken "a lot of effort" to cover the paintings.
Police said they would be checking CCTV to see if they could find the culprits.
The first painting, of a sleeping child, was commissioned five years ago.
"The park was derelict at the time and it represented its awakening," Mr Evans said.
"People loved it, it was the park's emblem".
The other two paintings, each done by Kings Heath artist Title, represented the park's history - a portrait of William Cadbury, who gave the land to the community, a tram, a public house and some local businesses, were finished 18 months ago.
"Stirchley's residents are up in arms," Mr Evans said.
"I think the paintings were deliberately targeted as every piece of imagery has gone."
Peter Walker, chair of the friends, said members of the group had been working tirelessly to improve the park for everyone and appealed for people to go to the police if they knew anything.
Since the vandalism was discovered on Saturday morning, Mr Evans said he had about 300 messages from people offering sympathy and suggesting fundraising ideas.
Three murals in a Birmingham park have been painted over, leaving residents "heartbroken" and "gutted".