Contacting the authorities is important. I suspect this person has a prior record of sexually offenses. Failing to contact the authorities may put other youths at risk.
This is not intended as individual legal advice and there is no attorney client relationship established by this answer. It is advisable that you seek individualized legal assistance. This is not a substitute for hiring an attorney.
Save all the Internet communication and bring it to the local police department for prosecution. If they do not act then bring it to the District Attorney.
Contact your local DA. At minimum, he can be charged with Corruption of Minors. The solicitaion over and the sexual photos over the internet may give rise to more serious charges.