A new hobby—combining arts and crafts fun, hide and seek skills, and an online tracking component—has taken Gloucester by storm.

Tracy Sweat of Gloucester started the Facebook group Gloucester Rocks just a few weeks ago, and it’s already grown to more than 1,800 members.

Simply put, the activity involves participants painting rocks with inspirational words and/or cute designs and then hiding those rocks somewhere in plain sight in locations around the community.

“Rockers” can then leave hints about the location on the Gloucester Rocks’ Facebook page to help others try to find them. The person who finds the rock can keep it going by picking another place to hide the rock, or can choose to keep it.

It’s a nationwide craze, as CBS This Morning reported in February on the hobby as it was sweeping through Ohio.

“A simple but unusual hobby is spreading across the Buckeye State,” the CBS News report said. “Residents are picking ...