BOSTON — A third employee of Massachusetts’ social services agency has been fired for her involvement in the case of a 5-year-old boy who has not been seen for months and is feared dead.

The commissioner of the state Department of Children & Families said Monday that an area program manager was fired after an investigation found she failed to ensure any follow-up after multiple reports of abuse and neglect in Jeremiah Oliver’s Fitchburg home.

A social worker and supervisor were dismissed earlier this month. In addition, Commissioner Olga Roche said another manager was given a three-day suspension without pay and removed from a decision-making position.

She said an internal investigation by the agency found staff missed multiple opportunities to engage with the Oliver family through home visits and sometimes went months between meetings with the family.

The boy disappeared in September, but police didn’t learn that until earlier this month. They are treating the case as a possible homicide.

The boy’s mother, Elsa Oliver, and her boyfriend, Alberto Sierra Jr., have been arrested. They have pleaded not guilty to child endangerment, abuse and other charges.

Roche said that the supervisor entered false information including that the children were well cared for and the apartment well furnished.

“This information was never available to them because they never visited the home,” she said. Roche said the supervisor knew that the home visits were not being conducted by the social worker.

She said the fired social worker had a comparable workload as another social worker who had worked with the family at a different DCF office and visited them regularly after they first became involved with the department in September 2011.

The care declined when the family moved to Fitchburg and their case was transferred to the DCF’s North Central Area Office in January 2013.