Emma Norton, aged 30, from Bentley, is asking for anyone with information on the dog's whereabouts to get in touch after he was snatched from outside The Jane Lane School in Churchill Road near the family's home on July 7 at around 5.45pm.
Simba, a golden brown teacup chihuahua, is a therapy dog to Emma's nine-year-old daughter Summer, who suffers from anxiety.
Since the dog was taken, Summer has been staying at her grandparents' house as she is too anxious to return home without Simba.
Emma said: "There is no way he could have gotten out of the garden as it is completely secure for the children, the only way we think he may have gotten out is slipping through the front door.
"This would be very uncharacteristic for him, as he suffers from anxiety himself.
"He has hidden around the house before when he is feeling nervous, sometimes for a few hours at a time. So at first we weren't worried but then we searched everywhere and he was gone.
"A witness said she saw a silver Transit van pull up outside Jane Lane School, a female in her late 20s to 30s got out with mousey hair and a child aged around 12 years old and picked up Simba. That's the last sighting we have of him."
The incident has been reported to the police who are waiting for CCTV footage, it has also been reporter to DogLost who are appealing for more information, a poster can be viewed on their website.
Emma added: "Every night I have been walking around the area trying to find him, posting on Facebook groups, knocking on doors. I'm not eating or sleeping.
"We are all beyond devastated, he is Summer's world.
"If someone can drop him off anonymously we won't take it any further. We just want and need him home."
Anyone with any information can contact Emma on 07701363971 or West Midlands Police quoting crime reference number: 20WS/159301E/20 the family is offering a finder's fee.
Alternatively, contact Crimestoppers anonymously on 0800 555111 or at crimestoppers-uk.org