Oakland -- Ask.com, the Oakland-based provider of Internet search services, said on Thursday that it will acquire Long Beach-based Lexico Publishing Group, the owner of Dictionary.com, Thesaurus.com and Reference.com, for an undisclosed amount of cash. Ask said that the acquisition will grow its network user base to more than 145 million unduplicated monthly users worldwide. It would rank Ask as the ninth largest web property, ahead of such prominent names as Apple and Facebook. "More than 30% of all searches conducted on Ask.com are in the reference category," said Jim Safka, the CEO of Ask.com. "At the same time, Lexico's consumers frequently seek out a search engine immediately before and after using one of Lexico's sites."