The fire department said a walker saw the body around 6:30 a.m.
Brandon vanished while swimming with friends on Monday afternoon. He jumped off a bridge into the rain-swollen Pennypack and was swept over a dam.
Brandon's 11-year-old brother Anthony was also in the water but made it safely back to shore.
Anthony has told police he saw Brandon waving his arms before he disappeared.
Generations have grown up swimming in Pennypack Creek on hot summer days, but they've all been breaking the law. Swimming is prohibited there.
"We've all been there and done it, disobeyed our parents at one time or another, unfortunately, sometimes things like this happen," Brandon Boyle's cousin Christina Pale said.
Signs are posted, but they don't last.
"As quickly as they go up, they come down," Pale said.
Even where the signs remain up, they're routinely ignored.
"When I grew up down here, we swam in the same creek that this young boy was swimming in; it's a rite of passage," Bob Brookes of Northeast Philadelphia said. "He wasn't doing anything that a normal kid wouldn't be doing."
It is a grim search that has been seen many times before on this creek. 17 years ago, teenagers Nick Simonetti and Chris Busse drowned after they jumped from the same bridge.
Three years ago, a 20-year-old man also drowned there.