Sending unsolicited commercial text messages is illegal under civil law. Other laws are often violated when spam messages are sent to numbers in the federal “Do Not Call” registry.

The commission said it was pursuing an additional case charging contempt of court against Phillip A. Flora, a serial text-message spammer who was barred in 2011 from sending unsolicited texts. He faces potential felony charges of violating a federal court order, in addition to a new lawsuit filed by the F.T.C. against his company, Seaside Building Marketing. Mr. Flora could not be reached for comment.

The authorities said it was difficult to catch companies that send spam messages because they frequently change the phone numbers used to originate the messages, making them hard to track.

Spam waves have become much more frequent since phone companies began offering unlimited text-messaging plans. Now, spammers buy hundreds of SIM cards, the chips that make cellphones work, allowing them to send a flood of messages and then abandon the phone numbers.

The F.T.C. has received at least 50,000 complaints about spam text messages in the last few years, including 20,000 that related to an offer of a free prize, and the number of complaints is growing rapidly. Mr. Baker said the commission received seven times as many complaints in 2012 as it did in 2011.

Officials advised anyone who receives such a message not to click on any link and not to reply. In particular, they said, consumers should not text “Stop” or a similar direction back to the sender, as spam messages often suggest; that simply lets the sender know the phone number is active and therefore a candidate for sale to other marketers. Instead, consumers are requested to forward the text message to 7726, which is a central repository for spam messages that has been set up by cellphone carriers. The message should then be deleted, the officials said.