* Second-largest shareholder says Bain offer too low
Top shareholder WPP also believes offer undervalues ADK -source
* Asatsu-DK supports Bain's offer, wants to end WPP alliance
TOKYO, Oct 5 (Reuters) - U.S. private equity firm Bain Capital LP's $1.35 billion offer to buy Japan's third-largest advertising agency Asatsu-DK Inc is too low, its second-largest shareholder Silchester International Investors LLP has said.
London-based fund Silchester, which owns 17.3 percent of the ad agency, joins largest shareholder WPP PLC in questioning the bid price, with WPP believing the buyout plan significantly undervalues Asatsu-DK, a person familiar with the matter previously told Reuters.
"The current offer price substantially undervalues ADK, its assets, franchise and future opportunities," Silchester said in a statement dated Wednesday. It "encourages other prospective buyers of ADK to come forward."
Asatsu-DK shares have risen above Bain's 3,660 yen ($32.49) per share offer price, closing at 3,845 yen in Tokyo trading on Thursday, indicating some investors expect Bain will have to improve its bid or that a rival bid is likely.
Bain declined to comment on the matter.
Asatsu-DK supports Bain's offer, saying private ownership represents the best option to position the ad agency for sustainable growth. It intends to dissolve its longstanding alliance with WPP, the world's largest advertising group.
Bain's latest bid for a Japanese firm comes only days after a consortium led by the Boston-based firm signed an $18 billion deal to buy Toshiba Corp's microchip business. ($1 = 112.6600 yen) (Reporting by Sam Nussey; Editing by Christopher Cushing)