Snapchat is down, as many users can’t post or send messages

Snap Streaks are at risk for the last few hours as users reported that they couldn't send messages or post stories on the site. Snapchat Support tweeted that there were issues and advised users to wait.
Although the source of this problem is not known, it doesn't appear to be a Facebook-level issue that will require a lot of time to resolve. The app is functional enough to use for most people. If you don't try to post, you might not notice any problems right away. Snapchat has not had to deal with the app crashing frequently, which was a problem. You may not require an update if service is restored.

Based on user reports, our experiences and a look at DownDetector, this problem is not yet fixed. However, if we get any information from Snapchat, or notice that things are changing, we'll update this post.