A bi-polar teenager in Westminster who touched off a frantic search as part of an arson investigation is now in custody.

Police say 15-year-old boy locked his stepfather in the basement of his home and then lit the house on fire.

"From what we have so far, the dad was in the basement and the son just locked the door that leads to the basement and lit the fire near the stairwell," said Westminster police spokeswoman Stephanie Topkoff.

The stepfather, James Misegadis, escaped through the basement window unharmed and went to a neighbor's house to call 911. Misegadis then went back into the house to rescue his three dogs.

On Tuesday night, he tearfully pleaded with the public for help in finding his son.

"He's a good kid. He's just got some issues he needs to work through," Misegadis said.

An arson investigator spotted the boy walking down the street near 64th and Federal Avenue.

The teen remains in custody at the Adams County juvenile detention center in Brighton. He will likely be charged with arson and attempted murder, 7NEWS reported.

The fire, which started at about 3 p.m. Tuesday in the 8000 block of Clay Drive, was quickly extinguished. There was no visible signs of fire damage from the outside of the home, 7NEWS reported.