"Couldn't imagine that our running community was being attacked in that way and it was really hard to accept," said the run's organizer Jennifer Reuland.
"I hope the folks in Boston know that we here in San Francisco, and indeed around the world, that we are behind them. We stand behind them 100 percent. And they should know that they're not alone," said runner Bob Saka.
James Geshwiler lives outside of Boston and was in San Francisco for a conference.
"Thank you San Francisco. This is very sweet. This is touching. I, it's very sad and thanks all of you for showing nice moral support. It's really terrible what's going on," he said.
The run was about four miles; from the Ferry Building to Aquatic Park and back. The mood was celebratory as runners cheered for each other at the finish line.