Facebook tumbled to a record low on concern that businesses are spending less to advertise on the world's largest social-networking website, according to freep.com.

The shares of Menlo Park, Calif.-based Facebook fell 5.4% to $18.06 at the close in New York. The stock has lost more than half its value since Facebook sold shares at $38 apiece in an initial public offering May 17.

"Checks on near-term paid media spending remain challenged," Daniel Salmon, an analyst at BMO Capital Markets in New York, said in a research report Friday, Aug 31. He has the equivalent of a sell rating on the stock and cut his price estimate on Facebook's shares to $15 from $25.

Facebook may post $5.04 billion in sales this year, EMarketer estimated, down from the market researcher's earlier projection for $6.1 billion as the biggest social network struggles to sustain advertising growth.