Former MLB superstar Darryl Strawberry says his teenage granddaughter went missing Wednesday in Nevada ... and the 8x All-Star is pleading for help finding her, and prayers to keep her safe.

59-year-old Strawberry took to social media to get the word out, writing ... "This is our granddaughter MyLisa who is missing right now! Please Please Pray for us as we desperately need your prayers! Thank You!"

MyLisa -- who was born in 2007 according to an online bio -- was last seen on September 22 around 7:15 AM. She was wearing all black at the time ... with a pair of white Jordans.

MyLisa's mom is Darryl's reality TV star daughter, Diamond Strawberry.

Diamond also went to Instagram to ask for help.

"PLEASE REPOST!! PLEASE SHARE!!!! Please help us bring MyLisa home!", she wrote, along with a description of MyLisa.

If you have any info on MyLisa's whereabouts, the Strawberry's are asking people to please call the Henderson Police Department at (702) 267-4555.