There are numerous websites that can help considerably when analyzing a WordPress target. Some of the most popular include:
What WordPressTheme Is That?
What WordPress Theme Is That is a free online tool allows you to easily detect what WordPress theme a site uses (including parent and child themes). Additionally, it will also detect what WordPress Plugins are being used.
Online WordPress Security Scan for Vulnerabilities | WP Scans
WPScans.com is an online WordPress security scan for detecting and reporting WordPress vulnerabilities.
WordPress Security Scan
Online WordPress Security Scanner to test vulnerabilities of a WordPress installation. Checks include application security, WordPress plugins, hosting environment and web server.
WordPress Security Scanner
WordPress Security Scanner checks if full WordPress version info is revealed, if readme.html file is accessible via HTTP, if response headers contain detailed PHP version info, tries getting the list of usernames, for display of unnecessary information on failed login attempts, if admin interface is delivered via HTTPS and much more.