Salesforce.com Inc., the largest maker of online customer-management software, plans to offer $1 billion in convertible senior notes in a private placement to institutional investors.

A portion of proceeds from the notes, due in 2018, will be used for acquisitions, investments in technology and capital expenditures, the San Francisco-based company said Monday in a statement.

Chief Executive Officer Marc Benioff is expanding into tools for human resources and online marketing, paying $689 million last year for Buddy Media Inc., whose software helps companies place advertisements on Facebook Inc. and Twitter Inc. Benioff has said he’ll keep using deals to help accelerate growth by pushing beyond cloud-computing software for sales management.