Edward L. Leathers Community Park in Somerville, where a firearm was shown on Tuesday. The image is from 2012. (Photo: Todd Van Hoosear via Flickr)

Somerville High School students sheltered in place Tuesday afternoon and the Central Library was closed briefly as police searched for two youths they believed to be armed.

Police say a gun from that incident is missing, and warn residents who may stumble across it: “Citizens should not touch a suspected firearm. If a suspected firearm is found, call 911 right away and wait for officers to arrive.”

A caller at 1:20 p.m. Tuesday told police that a couple of minutes earlier he’d come across two young men on bikes in Edward L. Leathers Park who showed him at least one gun. The park is just across Medford Street and a set of train tracks from the library and high school, and the caller said the youths were riding in that direction, police said.

By 1:27 p.m. the park was empty, according to scanner reports, and officers were looking elsewhere for a masked rider in a black hoodie on a blue bike and another in gray joggers. The search was helped by a photo taken from surveillance video.

The high school was locked down by 1:39 p.m., though the shelter order was maintained only until around 2 p.m., according to scanner reports.

When a suspect was spotted in front of library at 2:16 p.m., officers “briefly detained” the person and found he was unarmed, police said.

A search of the of the area by Somerville police and National Park Services Police K-9 units found no weapon, leading to a warning for residents to avoid touching weapons they find, and to instead call 911 to report the discovery.

The incident is under investigation, police said, and anyone with relevant information is encouraged to call (617) 625-1600, Ext. 7250, or text a tip anonymously to TIP-411 (that’s 847-411 with “617spd” at the start of the message.