Twitter Inc posted a disappointing 7 percent slide in a closely watched measure of engagement even though its user base grew 23 percent in the third quarter, triggering a more than 9 percent decline in its stock on Monday. The online messaging service also projected fourth-quarter revenue that may miss Wall Street’s targets. Expectations had run high for Twitter since the messaging service, which for years had fought to revive growth in users, surprised Wall Street in the second quarter by signing up 24 percent more people globally.