The alert posted to Twitter Thursday night says police believe 16-year-old Amy Yu of Allentown and Kevin Esterly are in Mexico, and Amy may be in danger.
The two went missing March 5th, shortly after authorities were notified the pair may have been involved in a romantic relationship. Yu's family previously said the two met at church years ago, and Yu is friends with one of Esterly's daughters.
School records show Esterly signed Yu out of school 10 times between Nov. 13 and Feb. 9. Police say Yu had changed school documents to list him as her stepfather.
In a criminal complaint filed with Allentown Police, Esterly's wife said he withdrew $4,000 from her bank account and that his car and personal documents were gone.
Yu is about 4 feet 11 inches tall and weighs 90 pounds, while Esterly is 5 feet 9 inches tall and 185 pounds, according to police.
Authorities believe they may be driving a 1999 red, two-door Honda Accord with the Pennsylvania licence plate No. KLT0529.
Anyone who sees either of them is asked to call 911, local police or the Allentown Police Department at (610) 437-7751.
The Associated Press contributed to this report.