A suspect in the death of a 4-year-old boy whose badly bruised body was found in an empty Amityville, LI, home is on the run, Suffolk cops said yesterday.

Jonathan Thompson called 911 Wednesday to say little Adonis Reed was unconscious, but he was gone by the time EMTs arrived.

Cops said Thompson was the boyfriend of foster mom Lakisha Pitt, a social worker for disabled kids who took in Adonis and his sister, Nayamya, 6, in 2012.