My Foster Dog Olivia is Gone!!

I recently took in a foster-dog, a 90-lb. brindle English Mastiff named Olivia. She was very recently rescued and has been fought, bred, and abused. She is severely underweight, had several recent surgeries, and is generally in pretty rough shape. She wouldn't eat or drink for the first two days I had her and still wouldn't even take treats from me as of Monday. Her biggest challenge is that she is not socialized: she is afraid of humans (including me) and, because she was locked in a garage, basically everything in the outside world is new and scary to her. I have never cared for a more needy, vulnerable dog.

On Monday morning, as we were crossing Mass. Ave. (NW, DC), her harness came detached from her leash. (This is odd because she still makes me drag her out of the apartment by the harness, and the connection to the leash was strong enough not to come apart when I pulled her into the hall. Regardless, it came apart one way or another.) Once she realized she was off-leash, she started running, right out into traffic, and kept going. I chased her to the Capitol, and the Capitol Police followed her to the intersection of 11th and G SE, but then they lost her as well.

She's incredibly adept at dodging people, and she ran much longer and farther than I would have thought she could. Between the activity and her general anxiety, she is almost certainly hiding. She likes to hide in bushes; and, for a 90-lb. dog, she's pretty good at making herself invisible. She is not at all aggressive - when approached, she runs/backs away as much as possible, then just hides her face.

She was wearing a red-orange martingale collar and a black Easy-Walk harness. She had had my dog Leah's extra i.d. tag on her harness, but had gotten that off. (She's a veritable Houdini when it comes to getting out of collars and harnesses!) She did not have her own i.d. tag yet, so the only tag she has on is the one from her rabies vaccination. She probably has not lived here long enough to find her way back, but if you see her (or even just think you might have seen her), please call (617) 947-5627.

Please, please help me find this dog! Please post this somewhere (/everywhere!) and forward it to everyone you know, people or groups, in DC. I have already contacted lots of authorities, organizations, businesses, etc., but if you can think of anyone whom it might help to contact, please do send it - I'd much rather have people receive her information twice than risk their not receiving it at all. I would also appreciate any other suggestions for publicity or other ideas on how to find her.

Please let me know if you can do anything to help find lost Livvie!
Thank you so much!