Authorities announced an arrest warrant for 57-year-old Dewayne Baxter from Philadelphia.
Police arrested and charged the first two suspects, Kevin Blagmon and Keith Walter, in January.
Baxter and a fourth suspect, who hasn't been identified, are still at large.
Investigators have been unsuccessful in locating Baxter who is also wanted for a Bank Robbery in Philadelphia. Anyone with information on his whereabouts is asked to call the West Whiteland Township Police Department at (610)692-5100 or (610)363-0200.
Police say the four men entered the Zales jewelry store in the Exton Square Mall around 4:15 p.m. on December 27, 2013. The suspects created a distraction that led to the theft of more than $15,000 worth of jewelry.
Store employees tell police that three males entered the store and separated once inside, speaking to different employees about jewelry.
None of the men made a purchase before leaving the store.
Shortly after the suspects left, employees discovered two diamond rings, which were valued at approximately $15,000, missing from a display cabinet.
Anyone with information about the theft or Baxter's whereabouts is urged to contact the West Whiteland Township Police Department at (610)692-5100. Persons wishing to remain anonymous can call the tip line at (610)594-9057 or email@example.com.