MARIN COUNTY -- Although the official search for Veronica Ruiz was called off Wendesday night, hundreds of volunteers turned out this weekend to pick up the search effort on Mount Tam.

The volunteers have hiked numerous miles of trail on Mount Tam and, until tonight, had found no trace of her. Sunday’s search did turn up a backpack which may have been hers.

The search for the 25-year-old I.R.S. special agent as drawn a huge response from people wanting to join in the search. Ruiz’s sister Maricris Ruiz is coordinating the effort.

She said her sister was spotted at the entrance to the Blithedale trail in Mill Valley at 11 o’clock Monday morning. A second sighting put her at the West Point Inn nearly an hour later.

Maricris Ruiz said that Veronica was distraught after a recent breakup and that her official sidearm is missing. But it was not unusual for Veronica to carry her weapon when she hiked the popular trail, she said.

Susan Schustak often rides the trail and is familiar with the area.

“The mountain really has lots of nooks and crannies and you really have to respect how huge it is,” she said.

Maricris Ruiz said it is almost certain that her sister wandered off the beaten path, which is why search efforts were focused off-trail Sunday.

The search for Veronica will continue every day.