I've been looking up statutes, but can't seem to find the answer. In MO, what happens if you get caught street racing? Do they just slap you with a massive fine and points on the license? Impound your car? Jail time?
One of the consequences in Missouri and it's pretty much the same as in other states is that...you can die and/or kill innocent, uninvolved people. In extreme cases they will execute a search warrant and go through your social media and browser history and locate examples of you asking about the consequences of street racing.
It is likely regulated by city/town ordinances instead of state law. In most states, you'd receive a 6-point violation and a fine ranging anywhere from a few hundred dollars to a few thousand dollars. If you cause injuries from engaging in this behavior, punitive damages would be appropriate.
You would also probably be hit with Reckless Operation and as others have said, if you cause an accident or injury, some sort of negligent, reckless, or purposeful vehicular assault that could be a felony.