Jessica Chastain thanks power of social media for safe return of grandmother's lost dog

Jessica Chastain has expressed her thanks to fans on social media after helping the actress track down her grandmother's lost dog.

The Help star took to her Instagram account on Thursday (21Jan16) to urge followers to help her locate the missing Maltese terrier after little Livvy was snatched outside a McDonald's fast food restaurant in Vallejo, California.

She even offered up a reward for the pet's safe return.

"My grandma's dog, Livvy, was stolen last night from McDonald's at 2565 Springs Rd Vallejo, CA," she wrote beside a photo of the pooch. "Please forward this to anyone you know in CA (California). There's a REWARD for Livvys (sic) safe return.

"For those of you who love animals, you must understand how devastated my grandma is. Please help."

Word spread quickly on social media and Jessica's grandma was reunited with her beloved Livvy on Saturday (23Jan16).

"Livvy is FOUND," the 38-year-old beauty revealed as she updated fans. "My grandma picked her up a couple hours ago. Thank you to each and every one of you that spread the word and put attention on this."

"I truly believe you all are the the guardian angels that reunited these 2 beauties," she added. "Much love to you."

Jessica isn't the only celebrity to recognize the power of social media - Mark Ruffalo was also able to have his cell phone and wallet safely returned to him on Saturday after losing the items on the streets of New York, in the midst of the heavy snow of Winter Storm Jonas.

Sending out a desperate Twitter appeal to his 2.1 million followers, Mark wrote, "APB (all-points bulletin) out for a cell phone in a wallet case out on the streets of NYC in a blizzard. My drivers license is in there. Reward and signed pic".

Just four minutes later, Mark returned to the micro-blogging site to reveal his belongings had already been found.

"OMG (oh my God) It was just found!" he exclaimed. "That was freaking fast. Thanks for helping me find it!!"

He then tweeted a photo of himself with the two young fans who had found his wallet and phone, adding, "Thank Amenaide and Catherine Brown for finding my phone and wallet! Thanks Brown family for your decency!"