OAKLAND, Calif. — One message on the web forum asked neighbors to be on the lookout for “two young African-Americans, slim, baggy pants, early 20s.” Another warned of a “light-skinned black female” walking her dog and talking on her cellphone.

“I don’t recognize her,” the post read. “Has anyone described any suspect of crime like her?”

These postings appeared on the Oakland forums of Nextdoor.com, a website intended to be a virtual neighborhood hangout for the tens of thousands of neighborhoods and hundreds of local police departments that use it to communicate with residents. The site’s chief executive and co-founder, Nirav Tolia, describes it as a place to find a babysitter, a plumber or a missing cat, and to have a “kind of ‘Leave It to Beaver’ chatter.”

But people also use it to report suspected crimes. And as Nextdoor has grown, users have complained that it has become a magnet for racial profiling, leading African-American and Latino residents to be seen as suspects in their own neighborhoods.

In response to the complaints, the company has begun testing ways to prevent these kinds of postings.