Messaging app Snapchat Inc has raised $1.81 billion in an equity offering, indicating strong investor interest in the company despite concerns that it is struggling to attract advertisers.

Snapchat did not disclose its valuation in the latest round of funding in its filing on Thursday.

However, technology website TechCrunch reported on Monday, citing sources, that the company could be valued at about $20 billion.

Snapchat, which makes a free mobile app that allows users to send videos, photos and messages that vanish in seconds, has faced concerns that the company's estimated valuation is not justified because of its uneven revenue stream.

Investors in this round included General Atlantic, Sequoia Capital, T. Rowe Price, Lone Pine and Fidelity, among others, TechCrunch reported on Thursday, citing sources.

Snapchat was not immediately available for comment.