BANGKOK, May 15 (Reuters) - Shares in energy companies and firms linked to Thailand's opposition Pheu Thai party, which came second in an election on the weekend, fell sharply in early trade on Monday.

The Pheu Thai party, backed by the billionaire Shinawatra family, won the second highest number of parliamentary seats on Sunday, but it had been expected to place first on the basis of opinion polls during the campaign.

Its candidates for prime minister included Srettha Thavisin, who was CEO of property developer Sansiri Pcl, which fell nearly 10%, compared with a decline of 1% in the overall market.

Another Pheu Thai candidate, the daughter of former premier Thaksin Shinawatra, Paetongtarn Shinawatra, is the largest shareholder in another property developer, SC Asset Pcl, which saw prices fall 7%.

Pheu Thai and its previous incarnations had won every election since 2001.

The liberal Move Forward, which placed first and even won in traditional Pheu Thai strongholds, has pledged to curb electricity prices and dismantle monopolies.

Energy companies, Gulf Energy Development Pcl, fell 7.6% and Global Power Synergy Pcl fell 4%.

Although Pheu Thai and Move Forward were in the opposition, a partnership between the two in a coalition is not guaranteed. (Reporting by Chayut Setboonsarng; Editing by Robert Birsel)