PITTSBURGH (AP) _ Juvenile charges of kidnapping and abduction have been filed against a 14- year-old girl who disappeared nearly two weeks ago along with a toddler she was baby-sitting, authorities say.

The Charles County, Md., Sheriff's Department filed the juvenile charges Thursday against Tammy Lynn Giles, of Waldorf, Md., after a nationwide search failed to turn up the girl and 21-month-old Michael Fitzgibbon.

''We're hoping this action will help smoke her out,'' said Sgt. Casey McDevitt. ''Now if anyone shelters Giles, he or she could be charged as an accessory'' to the crime.

Meanwhile, Michael's mother came to Pittsburgh on Wednesday because Miss Giles' boyfriend is scheduled to be released Sept. 13 from a state prison outside Greensburg in neighboring Westmoreland County.

Sharon Fitzgibbon, 34, of Waldorf, Md., said there were reports that Miss Giles had told others she was planning to meet her boyfriend after his release.

Miss Giles has run away 22 times since January 1984, Mrs. Fitzgibbon said.

The girl is ''extremely self-confident and able to move. She could very easily be in California by now,'' McDevitt said. In previous trips, Miss Giles has been found in Texas, Tennessee and California.

A police official saw a girl fitting Miss Giles' description - 5-foot-2, 120 pounds, blond hair and blue eyes - in downtown Pittsburgh on Wednesday with a baby. Michael is 30 inches tall, weighs between 27 and 30 pounds, and has blond hair and brown eyes.

Pittsburgh Police Capt. Therese Rocco, head of the Missing Persons Bureau, said detectives checked out more than 25 tips Wednesday and Thursday.

''At this point I don't know what to say,'' Rocco said. ''With all the good publicity we've been getting, you'd think something tangible would have surfaced by this time.''

Miss Giles was watching Michael at the Fitzgibbon home Aug. 4. She and the baby were discovered missing the next day.

''I'm going to stay here as long as I have to until he's found,'' said Mrs. Fitzgibbon.