Stephen Fry, footballer Rio Ferdinand and Sarah Brown – wife of ex-Prime Minister Gordon Brown – posted links to appeals for information about Serena Beakhurst.
Police said the 14-year-old, who also goes by the surname Dennis, disappeared on December 15 after catching a bus from Herne Hill Station in south London to attend her beauty therapy college course.
She has never been reported missing previously, police confirmed yesterday.
On Monday, the Metropolitan Police said it had "exhausted normal lines of inquiry" but yesterday said they were about to re- interview the teenager's friends.
Other celebrity Twitter users involved included actor and writer Simon Pegg and Matt Lucas. of Little Britain.
Serena lives in Tulse Hill, south London.