Cynthia Frank is one of a growing number of pet owners using social networking sites to show off their animals and connect with other pet lovers.

Since she and her husband separated, Frank can’t be with her dog, Scout, every day, but she can share news about her and get updates on Dogbook, a third-party application of Facebook.

“It left a big hole in my life when she went to live with my husband … then we got connected on Dogbook,” said Frank, 58, of Silver Spring, Md., who also maintains a profile of her cat, Cinnamon, at Catbook. “The fun part is that I can send little messages to Scout,” which are read by friends.

Frank says she can give the pup virtual hugs and scratches behind the ear. She’s also been able to hook up with old friends and their pets through the applications, including a woman she went to high school with and her cat. “It makes me feel like I’m more connected,” Frank said.

At Dogbook, canine owners can create Facebook profiles for their animals, find dog parks and products, and tag their dogs in photos. Major advertisers on the app include Purina, Toyota and Coke.

Geoffrey B. Roche, co-founder of Poolhouse Enterprises, which produces Dogbook and other pet pages, said the idea came to him a few years ago at the dinner table, and took off quickly. Now, there are about 2 million users on Dogbook and about 1 million on Catbook, he said.

The sites work, he thinks, because people see their pets as more than just animals.

“The dog goes way beyond what was just a dog. It becomes a family member,” he said.

“This is a great way to keep track of pets’ lives.” Users “are as excited to show you pictures of their dog as much as their kid, if not more,” he said.

Dogbook’s recently launched iPhone application passed 80,000 downloads after just two weeks.

Brandee Barker, a Facebook spokeswoman, said Dogbook has nearly 800,000 active monthly users, followed by about 175,000 on Catbook, 31,000 on Horsebook, 3,900 on Rodentbook and nearly 1,900 on Fishbook.

“From the beginning, our goal has been to provide a platform for people to connect and share about anything that might interest them, and clearly people are very passionate about their pets,” Barker said. “So, I think it’s a natural extension.”

Facebook doesn’t allow pet profiles on its main site, where it tries to foster “the real-name culture” and keep up security, Barker said.

Other social networking sites, including Twitter and MySpace, also allow people to post updates and create profiles for pets. One popular cat page at Twitter goes by the handle “Sockington” and boasts more than 1.5 million followers who receive Sockington’s (or Sockington’s owner’s) random thoughts. At MySpace, there are thousands of pet pages and nearly 200 pet-related applications listed in its applications gallery.

Pet-related businesses are using social networking sites to reach and educate customers. For example, PETCO has more than 15,000 fans on Facebook, and joins conversations on Twitter in which customers ask each other and the company questions and share advice on products.

Natalie Malaszenko, director of e-commerce for PETCO, said establishing a relationship with customers is good for business. “It helps us to have an insight and a seat at the table in the life cycle of their pets,” she said.

Karen Pudelski, a dog and cat owner from Harvest, Ala., who owns a pet sitting business on the side, said she had been going on Dogbook and Catbook only every few months to update her pets’ profiles, but now has become a more regular visitor because of the iPhone application.

The sites are a great way to find pet-friendly businesses or dog parks, she said, or just chat with other pet lovers.

“It’s a great way to connect and meet new people who are just like you … animal lovers, or a way to find a play date for your pet,” said Pudelski, 43.

Pudelski, who has two daughters ages 13 and 21, said she has fun posting to her pets’ profiles, and virtually throwing a bone or sending a dog toy to business clients.

“My kids laugh at me — I have pictures of the dogs in my wallet but I don’t have pictures of them,” she said.